That's human instinct just like girls that are attracted to buying make-ups and clothes and stuff. Maybe, that's what they enjoy doing and it makes them manly enough to do those kinds of stuff. It makes them as a real man and maybe feel superior and satisfied. But, there are men who don't watch pornographic videos, too and I respect them a lot. It takes a lot of self-control and discipline for them not to be influenced and tempted by others. As you know, men are men and they have all the reasons in the world to do feel and do so as related to their being "manly"!