Whats the deal with guys cheating on their pregnant girlfriends/wives?

I think if that was to ever happen to me and I was pregnant. I would so dump the guy and say i want child support when this baby is born but I want nothing to do with you ever again. I think they think women who are pregnant don't want sex due to the fact that she has a baby growing inside of her and he doesn't want the responsibility. Good Luck with more answers.