I've wondered this too. Is it in part though that we now diagnose all these different ailments? Maybe they've always been there but, they were lumped under other more blanket terms in the past. Or, they weren't even recognised.
I once took a tour of a WWII submarine and people on the tour asked our guide- who was a navy veteran- whether they suffered from SAD or depression and he replied that- they basically weren't allowed to! It wasn't even recognised.
When assylums existed in the UK, you could find yourself being committed for a whole number of different symptoms. Some of which we wouldn't even find indicative of mental illness now:
Insane asylums were big business back in the early 1900s, and nearly anyone could be declared "insane" and sent to an asylum. In a newspaper report from
listverse.com
I do know what you mean though. During my school years, there were maybe 2 or 3 children in the class who were described as 'special needs' and who would receive more tuition. Maybe the odd behavioural issue here and there. I know teachers now who have multiple serious cases of behavioural issues including violence. It does feel as if there are more cases.
I think you're right too- I think it's a combination of the unnatural lives we lead. The amount of competition from an early age. I think social media has done as much harm as good. Plus, I just think our physical environment is full of pollutants. We're likely all breathing in and drinking/ eating micro plastics. That shit can't be doing our bodies/ brains much good- not to mention our processed food diets.
Plus- I expect a lot of things are hereditary. We've effectively bypassed natural selection so that (sorry for the maybe offensive phrase) 'defects' are allowed to prosper. Not that I support eugenics or anything but sometimes I have to wonder. Like I've known people who I believe to have likely hereditary mental illness like bipolar really want children. Honestly- being antinatilst myself, it just puzzled me. Like- aren't you at all worried they'll end up suffering as much as you have? Obviously- I didn't say it out loud. Ultimately- I'm more pro-choice when it comes to others but- it puzzles me nonetheless. I'm glad no child has ended up with my genes!