Plus, our brains literally trick us into feeling better by complaining about things. So you get all the happy feeling about “doing something to improve the situation

One can make constant, meaningful improvements to all aspects of their personal situation and still have valid reasons to be depressed.

I feel that it is a perfectly normal reaction for one to be discouraged when they are overly limited by the world around them; while the people who are mostly not limited do absolutely nothing to put anything back into society (in practice, they are mostly doing the opposite).

without putting in any of the work.

Not everybody is capable of putting in the work you feel is necessary to empathize with them.

If you aren’t going to do the work to improve things (both yourself [...]

It's society's job to do better - as a whole. It is likely desirable for society for individuals to take responsibility for their actions and to do what they are able (at their own pace), and hopefully be given the freedom, support (if needed), and allowed the opportunities and circumstances to do their best.

Sometimes just existing is all that somebody can do at certain points in their healing journey and I feel it is desirable for us to accept that - safety and stability can be provided regardless of personal effort or externally visible effort.

[...] and the world)

Individuals putting the weight of the world on their shoulders likely isn't beneficial for their physical or mental health.

the distinction of the cause doesn’t matter anyway.

The distinction always matters. There are many, many reasons why people develop mental health disorders; that is why the chemical imbalance theory is mostly debunked - it's overly simplistic. This belief likely reinforces stereotypes and narrows treatment focus.

I firmly believe trauma and other environmental or physical health causes are discounted in most mental health treatment.