I really liked the Advance Wars series. It was extremely fun, and still has some passionate fans. I am sure all of the games turned a profit. Was it ever a mega seller? Nope.
In the end there are games out there we would all like to see sequels to. But if they aren't one of the top selling games, then there may not be a compelling business reason to make a sequel. The resources are probably better spent trying a whole new type of game from scratch.