The reason I create games - which is not in your list - is for the challenge of doing so.
The pencil, paper, dice rpg is basically a design challenge. You have very limited resources and yet a lofty goal: create a game which is better than D&D - faster, more realistic, and more engaging - without simply recreating D&D. It's a bit like playing Jenga where each rule is a block you add to the stack and then to slim the system down you remove what you can, all hopefully without causing the system to crash.
It's also a good way to get inside the mechanics of a game, to understand why one system would do initiative one way while another system does it in a completely different way. Unfortunately, there is that necessary slimness that a game needs to have which doesn't allow for the designer to stick in notes about why things are the way they are. If you can't just ask them directly then the best way to get to these answers is to take the game apart, largely by building something similar to it.
I am one of the "Yes, but only for my own use" types. I have built and trashed at least a dozen systems since 1993, having never done anything but some meager playtesting with a close group of friends who really would have rather been playing something else (but hey - favors). The reason I've never ventured past that point are all the other reasons mentioned in the post. The frosting of images and layout costs money which will probably not be returned by sales. The fame that comes from being a game designer is dubious in certain circles. And - on top of it all - you have to contend with the herd mentality which only wants to play what everyone else is playing, which right now is D&D.
To sum it all up. This may sound strange but I do it for fun and while I will not give away my fun work for free, the fun generally stops at the point where designing a game becomes a business. There are better businesses one can be involved in.