I think that a significant factor in the cross section of "need purpose" and "work = purpose" comes from a sort of brainwashing though. When you're taught (intentionally or otherwise) that amount of money, marketable skills, monetization of hobbies, etc all directly correlate to your worth as a person, it's absolutely surprising nobody that people who stop working (whether through retirement, disability, having children, etc) become depressed.

I totally agree with you, except for the part where you say that it isn't dystopian. A utopian society would be beyond that frame of mind imo and retired people would feel free to explore hobbies and passions, feeling more fulfilled than they ever did selling their labor for survival. I don't think these people want to go back to work; I think they want to feel useful. And they've only ever felt useful as workers. They can't imagine any other productive use because they've never experienced it.