Making collages is a kind of building too.

It tends to be people that enjoy their work. I know a retired TV comedy writer in his 80's that continues to meet with, edit for and make industry introductions for young writers just because he loves storytelling and comedy writing.

I agree with richiea that it is people who enjoy what they do and even though it has provided them the means to choose not to do it any more, they continue because they like it.

I'm the kind of person who writes code for fun. I like solving puzzles and coding is the ultimate puzzle solving game, not only do you get to solve the puzzle you get to make up the pieces you are going to use to solve the puzzle and so can solve it in infinitely many ways. Paid or not I'll spend my "free" time writing code and designing circuits.