For me, the basketball version is fun to work on because I'm a huge basketball fan. Other sports wouldn't be nearly as fun for me. If I thought that making versions for other sports was the path to riches, I might be motivated enough to try it. But if the basketball version can't grow beyond its current popularity, then the other sports probably won't be hugely profitable either.
That being said, I am working with someone to make a baseball version, but it's too early to say if anything worthwhile will come from that effort.