Because I like dwarves and I never made a dwarf game Also elves digging underground cities doesn't make sense to me. Goblins would be cool, thinking of doing a goblin game too one day.
No I can not see "almost all indie games only have dwarfs and nothing else". Are we looking at the same website? Do you have all search filters turned off? I have the feeling you are the one obsessed by dwarves.
It would take a big paycheck to do things I don't like in my free time, instead of having fun and enjoying my artistic freedom.