Why do men cheat on Preg wife?

Ok, is this common? Men cheating on their pregnant wife? The reason I ask is because I am up to 5 guys I know of that have done this. This one guy just told me his wife is a B and he can't stand her and there is no ...so he hooked up with a 26 year old girl for the fun of it. Mind you he has a 4yr old right now and he's doing this. Another guy just told me its the perfect time to do it. And another guy told me he did it because he couldn't take it not having and he was not attracted to his wife. One guy told me his wife caught him cheating and after the baby was born they talked about divorce right away but its on hold right now. Terrible. So what's up? Is this a popular thing to do????? geez!