Generally people do things for one (or more) of the following reasons:
1) Personal gratification (it brings them joy to do it)
2) Glory (they like the attention and praise they get from doing it)
3) Financial (they are able to earn an income from doing it)
In my case, I do it for all 3 reasons. I enjoy making things like DesktopX widgets for instance. It doesn't generate any money but I do like it.
I also like seeing how people from all around the world are using what I've made. I just think it's so cool to find someone I've never met in Japan or Poland or Australia using what I've made.
3) I'm fortunate in that I am able to make a living in this area. This is sometimes a bitter pill for others as I have made posts that are almost identical to someone else promoting their "free" thing but because some people know I make a living doing the kind of thing others do for free I'll get flamed. That's a bit of a bummer but I am still glad I get to work on things I enjoy for a living.