Why are men attracted to lesbians?

It's just a stigma in society. Most straight guys enjoy or like seeing lesbians make out, but are not cool with gay guys doing the same because they are of their same gender, and the fact according to modern day society a man is supposed to act manly and not feminine like. It's more looked down upon than lesbians. I really don't understand it, to be honest It's ridiculous, to say the least. It's really not fair -- I'm a bisexual girl, but I love my gay and lesbian friends just the same.