https://en.wikipedia.org/wiki/Hedonic_treadmill

A little of the above and a lot of not wanting to starve to death.

In graduate school I used to go out drinking six nights a week, the kind of thing that would start at 5 pm and end at 2 or 3 in the morning at somebody's house doing bong hits. Thirty years later, I would choose waterboarding before I put myself through that again.