It's what they're attracted to, and you can't stop them from being attracted to them. You can't really blame a gay man for liking dicks just as how you can't blame a lesbian woman from wanting to lick pussies.
Dicks, dicks, and more dicks! It is what every gay man wants to see, and just because he has one himself, doesn't mean he doesn't need to get his hands on someone else's dick.