Part of developing the game is knowing what your audience wants from your product. As long as the additional content does not completely overtake your original vision, what's the harm in adding a bit of it?
I do agree that incest and NTR is overdone. I'm especially tired of seeing mother/son incest, and I have zero understanding as to why anyone would want to be cucked. I like having all the pussy all to myself.
Even if I didn't have a pregnancy fetish, I could still say it is not done especially often and is rarely done well. If it isn't a bad ending, it is made as a "several months later" epilogue and you'd be lucky to get more than one scene. You could probably count on one hand the number of games that handle pregnancy in a way that makes any amount of sense and provides additional content, like Violated Heroine or Twin Quest. Summertime Saga and L&S: Second Base are both limited but getting up in there.
