1/ people who come to it later in life, for whom it's mostly a profession;

2/ people who start very early due to some desire to e.g. hack a game

3/ people for whom programming is a means to do things;

4/ people who just love programming for some ineffable, aesthetic reason.

This isn't an exhaustive list, but I know a lot of people who sit in (2) and (3), and therefore ultimately move away from computers into e.g. people/project/product management, gardening, technical support, sales, IP law, etc.. For me, like the author of this post, I don't think I can ever imagine not programming -- I get a sense of almost mystical excitement and satisfaction out of the act of writing code. I don't programme in my professional life anymore (I'm a founder and a CTO -- I have a lot of other things to push forward) but I always have _something_ I'm working on because it's a different type of problem solving, a bit like playing music.