Quick question: Pregnancy?
That's all I can hope for. The Impregnation fetish finds itself in this weird valley between the objectionable fetishes and the ones adopted by most people. It's not bad, hell some consider it a base instinct. However, it heavily favors men over women which loses 25% of people by default most times, and some associate it with others like the oh-so strange childbirth tag. There are games on this site that have it in it, unfortunately. Then there's the fact that, in vanilla novels, how do you justify it in a realistic fashion? As a result, it's rarely explored.
Doesn't help that it often relies on either writing or an extra overlay addition, where the former, as I said before, requires more effort than you'd think. This is because talking about stuff like babies during sex can sound weird and disjointed. Meanwhile, the latter is only really slapped on there for the free extra tag on R34 rather than anything interesting.
If you could give it some more depth and dialogue than other games, even as a side option, then a lot of people would be in your corner. It's just a difficult feature to incorporate compared to most.