I don't think there's a motive, atleast not one that is operating at a conscious level, per-se. People in any civilization are inculcated with a set of beliefs just as members of a cult - they are raised with a rather static lens they are taught is the "correct" way to experience, perceive, and make sense of reality; this can be something as simple as "things fall down because of gravity", to "money is a very important pursuit in life", or "communism is evil". Taught repeatedly both explicitly and implicitly, one begins to lose themselves in these messages, and the differentiation between "self" and this static perception becomes very fluid - an attack on this perception, even in the form of a piece of information that creates a stark juxtaposition, triggers a fear response, much like that of an animal encountering a predator. The idea is, we may have incredibly advanced technology, but we still operate psychologically at the level of tribespeople; we become incredibly attached to cultural belief systems the same way we attach to our mothers and fathers as children, even if they abuse and berate us.
This comes to the heart of the problem, in my mind. Our cultural apparatus no longer seems to have answers for us, and the chase of money, status, materialism, et al - the hollow idolatry of late capitalism - is failing writ large to satiate our existential fears, if in large part because the system pumping it out has become so corrupt and inequitable that it is losing its legitimacy, and with it, its ability to hold us under the "civilized" spell. But even so, you have billions who have been raised to believe in its wicked fairy tale, to see and judge themselves and others through its objectifying, atomizing, reductionistic lenses, and for the most part know no other way to perceive reality. This is a large part of why "mental illnesses", suicide, and childlessness have skyrocketed and continue to - these are perhaps natural reactions to perceiving reality accurately, beyond any cultural spell.
This said, how does one continue to exist in a world that is not only rapidly changing for the worse - where an extinction crisis is looming large not so far over the horizon, where one is more likely than ever to be socially isolated, exposed to toxic levels of pollution, live in a terribly unhealthy fashion, work an unrewarding, mundane job that barely pays enough - and NOT want to kill yourself, or at the very least be chronically depressed?
Well, the answer, which also includes the answer to your question, is to double-down and become even more insane in the ways of the culture. The role of culture itself is transcendence - to deny death itself and give life a sense of permanency; culture becomes the self and the self becomes culture, but by becoming so intertwined, one becomes a part of its hypervigilant immune system. The problem is, no one really benefits from this arrangement in the long run; but in the short run, the constant denial of reality keeps one in a state of blissful, willfully ignorant cognitive dissonance. To anyone not insane in the ways of our culture, anthropogenic climate change is the Sword of Damocles hanging over life itself, making everything we need to do to sustain life in modern civilization seem absurdly Sisyphisean.
And yet, the denial of reality serves a dual purpose - it allows one to sink into learned helplessness, and it allows one to avoid the existential crises that come with awakening to the fact they are utterly codependent and individually helpless (much like an abused child who ultimately conforms to its treacherous parents' whims, once it realizes they're the hand that feeds and it has nobody else). To illustrate, right now it is estimated some 60% of the world's population lives near a coastline, with nearly 2.4 billion people living and working within 100km, and some 634 million living only 10m above sea level. The majority of these individuals live in the mega-cities that themselves are the major arteries of modern civilization. These cities are neither sustainable nor self-sufficient, and depend on a fragile global logistics chain to continue functioning.
Imagine yourself to be a decently well-off middle class resident in one of these coastal regions, or cities. You have an advanced degree and a great white collar job - let's say you're a family practice physician at a small doctor's office and although you don't save much, you do make ends meet, have an alright social life, overall things don't seem too bad. You never struggle to put food on the table, you're relatively happy with your life, more or less. You feel "successful" in the eyes of your culture because of the two letters after your name, the size of your paycheck, the fact you "own" your property and a nice car from the last 5 years. You're the envy of your less fortunate friends and peers, who are struggling in the gig economy and paying $1100 for a bunk bed in a small room; they look at you and tell you, "you've made it, man!" - its a similar admiration you experience with the opposite sex, who perk up after you mention your career. So, things seem relatively stable in your life. Economic crises seem to come and go, the world seems to be getting scarier by the day but you don't notice much - sure, groceries are always getting more expensive and the packaged goods keep shrinking, sure, you keep seeing friends from your peer group drop off the map or appear in obituaries you scroll past on Facebook, regardless more and more of them are speaking openly of their "mental health" struggles, and sure, people seem to be driving a little crazier, more of your patients are uninsured or on Medicaid, and the weather seems to be more chaotic than ever. But for the most part, you get up in the morning, get dressed and drive to work like everyone else, and although you can't dismiss this tickle in the back of your mind that something isn't quite right, your life seems rewarding enough to keep the tickle repressed. You might get a surge of anxiety now and then - or maybe that's just another pothole on the slowly degrading, neglected highway you take to work, but eventually you forget it until the next time, and the next.
The point is, if you live in any measure of comfort like the above story, belief in the status quo IS your "self", it not only enables your life, it provides you a stable sense of identity and status. To consider climate change is to collapse that lens upon itself, reveal it as a dream, an illusion, and with it, everything you have come to see as fixed and rigid and sensible about your life, every answer you've ever had to those late night existential questions that keep you up. It is to awaken to the stark reality you are a helpless cog in a massive mechanism, who operates a machine you don't understand, that runs on a fuel you can't create yourself, to work a job that is only possible because of a global logistics chain, to shop at a grocery store full of food and drink from who knows where, made by who knows who, to return to your domicile in the evening powered by who knows what from who knows where - all you know is as long as you keep your bills paid, the lights will magically turn on, the food stays cold in your fridge, and you can veg out to the latest sitcom on Netflix after a long day at work. Besides, what could you really do about rising sea levels or a splitting polar vortex, individually?
If we return to the story, imagine yourself that person again - and you've brought up similar subjects with your friends, or your professional-class colleagues, but they tell you you're being a downer, so you eventually drop it, and maybe even begin doubt it's even real or that it matters at all. "The scientists will figure it out," you tell yourself, clutching the Bible that's actually a cellphone streaming the latest climate denial or techno-hopium to your eyes, as you drift off to a dreamless sleep. Anyway, you've got work in the morning and the clocks always ticking and the bills aren't gonna pay themselves.
It's far easier to accept the one reality that is farcical and mundane and be united with your atomized peers in that, to feel the power your status and money grants you, to do the steps of the dance of "normality" - than to stand completely alone in the other reality, in which you are a dependent child in an adult's body, subsisting in a world that is not only bewildering and complex beyond your imagination, but utterly terrifying and unpredictable beneath it all. In that reality there are no answers, only the fact that there doesn't seem to be a place for you in it, and your life is virtually unimaginable without the forms of modern civilization - the grocery stores, the gas stations, cars, two day shipping, fire and police departments. Most would sooner forget that is the world that is threatened and fading than imagine living in a world would it.
