[throwaway22032]

In my experience depression is in most cases basically a variant of burnout.

When people get stuck in a routine (job, city, hobby, political view, whatever) where they're focused mainly on the outcome rather than the process. Extreme long term thinking.

Alienation, that sort of thing.

It's common to say it's "under diagnosed" in places where people live more natural lives but I think this is correlation rather than causation.