Technically, men are not supposed to find pregnant women sexually attractive for the same reason why men who are married with kids often lose their sex drive. It is our evolutionary purpose to find a fertile woman and knock her up. Once we do that, our job is done, and we can lose our hair and get old and fat in peace. A woman who is pregnant cannot be knocked up by a man looking to breed, and so should not be a sexually viable target. However, we live in an age where hedonism is common and tacitly encouraged online, and people unironically jerk off to feet... Attraction is changing with every generation; probably for the worse if today's sex scandals and billionaire pedo cults are anything to go by. I could talk for hours about how the internet has normalized hedonism in the Western world lol.