>>718826316 (OP)
It's because it's hard to work with as a mechanic.
Most games with a "turn-based" style world mechanic use days, or in rare examples weeks.
Haramase Simulator has pregnancy last for seven weeks, but offers a realistic mode where it takes 36 weeks (still not accurate, but whatever)
Monster Girl 1,000 just has any girl you get pregnant go from flat-bellied to 7+ months along in the blink of an eye, even when mere days have passed. They won't give birth until the post game where you can choose to time skip a year. (your children don't grow up though. that would take too long to implement) Plus, he had to add a mechanic where you can use illusion magic to make your partner look non-pregnant for everyone who prefers that, and there are points in the story where characters mention how the pregnant characters shouldn't be fighting, which limits what can be done with them in a story sense. (though, most pregnancies only happen after a certain plot stage has been reached, so that's not an issue)
So really, it's a concept that works best as it's explored fully, where they explore the idea of two people preparing to become parents. But that means that: 1, Whatever story you were up to now has another path that can would need to be entered from any point, and either stop entirely, or continue anyway in the same way, which is rarely possible without just losing out on content. 2, the idea of impregnation has to be a mere afterthought only to pay lipservice. You creampie a girl, see that egg and sperm graphic, and cum really hard before you realize how much legwork your own brain had to put in to get aroused by that. or 3, the entire point of the game in a gameplay environment specifically suited to it (like Haramase Simulator, or most breeding season ripoffs, that usually don't even show the actual pregnancy)
