Another point is that people have their sense of self-worth tied up in their occupation.

I get paid a lot => I'm an important part of the world => if I stop then the world will fail (in some [tiny] way).

You see a corollary of this in retirees, their occupation defined them. Pre-retirement they say "hi, I'm Joe, I'm a professor" - a professor isn't a professor when they're relaxing and enjoying themselves (the thought process goes) so in order to be a professor I must work long hours at teaching students.