It is the tension and ultimately gradual corruption process of the heroine that holds an appeal, it makes character more alive and interesting, and usually sex acts more kinky and depraved. I have found both games where mc wins over a girl and where he loses the girl and a bull wins a girl (the real) mc fun to play. But very few creators can truly develop such genre, outside of writing small/big dick and making a girl jump for a bigger one.
It's the same reason why you have no interest to play a game where a girl starts as depraved slut and you just watch mindless sex scenes. The whole pursuit, conquering, competition, character development is what drives the fun.
Also, another reason why I probably enjoyed some games in this genre, is probably my massive dick size, when you have large size, you cannot possibly associate yourself with a tiny one - usual portrait of a cuck in those games.