I think there might be a component here of people able to reasonably achieve FIRE level wealth are already predisposed towards functioning well in the work place, and therefore maybe not so well suited for a life outside of that institution.

When I say I have projects I know I'll never do, I'm talking about the kinds of things that range from "will probably take several years" to "might not be completable in the lifetime I have remaining". Even if each of those things takes an eighth of the time I think they will, I still easily have enough to fill up the rest of my life even if I never do anything purely for the enjoyment of it.