I just like how they feel and they just look nice lol. Um, it makes you think the guy is strong and girls (well I won't try to speak for all of us) but generally girls like guys who have this "protector" demeanor. So if they're bigger than you and look like they can protect yo and you feel safe with them, a lot of girls are attracted to that
I personally love them because it shows that the guy cares about himself enough to work out. I just love the way that they feel comforting. When I hug a guy with nice abs, I can feel them and they just feel comforting and protective. As if no matter what he will always protect me.