I genuinely don't understand what's so sexy about a woman's stomach being bloated for several months while carrying her baby daddy's offspring inside her.
Also, since we're on the topic, I really don't get why some guys want to fuck/coom inside preggo women or suck breast milk out of their GF/wife's boobs.
The sexy thing is she's carrying a baby in there so someone's hoping to have a nice future and raise a child with her but you're there to bang her round pregnant belly and wake up the baby. Also the milk is nice