I mean, this is mostly just a personal opinion, but werewolves are just cooler? In erotic games(and a lot of other media, not all), vampires are depicted as humans with big teeth, nothing monstrous about them. With a werewolf character you can get a bit more: human, demi-human, humanoid wolf or just go full bestiality and just make it an oversized wolf. Werewolves also have more internal conflicts(as they are usually not in control while transformed), so it is easier for writers to give them character arcs and develop them, I'm not saying vampires can't have these, but it is a bit harder for beginner writers to implement them in an organic way.
As a side note, are there any erotic scenes with the MC in his werewolf form(if he even has one)? Because if not, then it feels like a missed opportunity, why even make him a "monster" in the first place if all he has are some oversized canines.