Correction, they turned a potential customer, into an actual customer for someone else. The ones that created the game lose out however, since you already played the game.

Just because you buy another game in the same genre doesn't mean they gained from it. Even games directly connection could potentially have different developers. Since the rights of games can be sold, and companies occasionally change or split apart.

Better yet, they impress you so much with their game that you illegally download, that you go out and buy from their competitor, instead of them, because you already have their game.