I think it's probably a lot simpler than that. The vast majority of people conflate being suicidal with being mentally ill, and the prevailing narrative is that what is considered mental illness is ALWAYS curable. They truly think everyone can be made better and get right back to work and being functional members of society, regardless of how feasible this actually is.
The severity of these ailments is also heavily downplayed, many people do not realize that eating disorders especially are deadly in their own right excluding any suicide risk. Unbeknownst to the people making laws, we have more "mentally ill" people than ever, and clearly current methods of treatment are failing many of the individuals who fall into these severe categories.
Most people think, if you can slap a diagnosis of a mental illness onto someone, they can always be cured. They do not see being suicidal as a "real" problem compared to physical diseases, not realising that people can become suicidal as a consequence of somatic illness!
In medical research literature, the economic cost of a disease is almost always brought up as some measure of how important it is to focus on studying it. Certain politicians want to abolish things like sick notes and force people to work and contribute as long as possible to the detriment of their health. Such motivations are a key part of the puzzle, yes, people in power truly believe anyone who is severely mentally ill can be fixed with some quick solutions and then enter the workforce again, to prevent a loss of productivity.
On the other hand, many suicide prevention organisations are not run by politicians with an economic motive, but individuals with altruistic motives who think they are doing a good deed and believe their mission is akin to firefighters putting out a burning building and rescuing people. They have good intentions deep down, but they just don't realize how ineffective hotlines and mindfulness pamphlets are for the vast majority of suicidal people who are not having "a moment of crisis". Even worse, many of these organizations support institutionalisation and believe that taking away people's rights and locking them in a ward is helpful and healing.
There are certainly politicians and economic-slanted professions who have a vetted interest in pushing more people back into the workforce no matter how miserable they are, that is true. However I think the biggest reason why euthanasia is still illegal for all cases in the majority of countries is because most people calling the shots in healthcare orgs are misinformed about suicidality and let their own personal beliefs cloud their assessment of other's capacity for decision making. Thus, they think everyone can be cured with enough hope, and anyone who says otherwise is loony/irrational.
If you want insight into this, read forums where doctors and those who work in mental health related fields converse online. There are so many of them who will brazenly admit that they lie to their patients because it goes against their personal beliefs to acknowledge that a suicidal person may be correct in their assessment of their own prognosis. Some of them secretly agree with patients, but don't want to be held liable for expressing any sentiment that is sympathetic to suicide or euthanasia. Many of them are well aware they are recommending useless interventions to patients whose problems are outside the scope of psychiatry, but once again they aren't allowed to voice this in the professional world.
I think there is just a deliberate, conscious denial of this uncomfortable truth, that some people could try everything under the sun to feel better and still be suicidal and longing for death. This belief that the state of being alive is precious and sacred no matter how much someone is suffering lies at the crux of why people are fighting back hard against MAID in Canada. Many of the people opposing it belief that the suffering is not real if it is "mental" and they are in complete denial of the hell that those whom they label as psychiatric cases experience in the day to day.