Labour is having to eat and clip your fingernails, having to sleep and repair the roof every year. All animals have to do it, humans always will have to do at least a bit of that, producing things just for them to be consumed. But work is building a world, and of course it does have to have meaning. An animal that won't breed in captivity doesn't want to survive under all circumstances. Sometimes even "nature" just says you know what, if I can only live as someone else's furniture, why live? Burnout is probably a similar mechanism.
"the remaining time"
Doing what is intrinsically valuable to you hinges on you still having access to the person you are. Don't take that for granted. A lifetime of settling can easily drive that out of someone, but planning to settle before it even started, as the only option, surely will. How could it not?
Old men [0] living it up because they never did while they lived is the worst. You can't regain a sense of justice, curiosity and innocence once you let it go and out of sight. You cannot have either without the other two, and none of them come back once you misplaced them as something you don't need "for now", but something very cringe and sad can takes their place, and it comes with this conspiracy of not mocking one another, of pretending to be fully featured people, as they stumble and babble into the sunset.
[0] And I say "men" because this is very much a male issue. You don't hear many women talking like that, at least I can't even remember one.