Doctors and lawyers can't do their work as a hobby. There are laws against that. But I can say from personal experiences that doctors talk about their work in their off-hours, usually in great detail, and over meals. Nurses, too.

Obviously, computer programmers can program anywhere, anytime, and it's legal. It's also possible to get a very early (as in pre-pubescent) start in actual programming, whereas there are, again, legal hurdles to becoming a doctor or a lawyer much younger than the median.

As for the rest of the cultural markers, I wouldn't presume to say too much, because I don't know that many programmers.