This is a harem game with 20+ LIs, and Allison is but one of them. Even if she has the most individual content (on account of being the "main" LI), the vast, vast majority of the content in the game involves people other than Allison. And so I think it's a stretch to say she's the entire reason for the game, as though none of the other LIs mattered. Maybe that's the case for you, but I would have thought that the dev—who has intentionally provided players with, again, some 20-odd other LIs—might have given us better control on who we could choose to romance. Especially since GILF in itself is not a particularly popular kink.
And at a glance, it seems like that was part of the plan at some point, since Allison has a point system. And what is the point of a romantic point system, if not to allow players to avoid that romantic path? If the dev didn't want people avoiding the path, why are there points?