I don't know what criteria must be met in order to have the game featured, but I do know it is put up by an admin and that the game must be popular in some way. Does the developer need to pay a fee to have the game featured? That may explain why most of the games we see featured are AG-related games.
Anyways, why a genre hasn't had a newly-updated featured game in a while is because no one has wanted to feature theirs.