Maybe because the idea of men having obsessions about lesbians is odd. They are, by definition, not interested in men. I simply do not understand the appeal. Unless you're all voyuers... >_>
Why do men like lesbians? And no, "because they're awesome" isn't an acceptable answer.
I actually considered this question before, and I think it appeals to a baser instinct for reproduction. Instinct takes less knowledge into account and more raw input; so when a man sees two women being explicit, to his instincts that's twice as many women to have children with creating a greater number of generations, thus a higher arrousal.
The double standard also makes sense, in that a woman seeing two men is useless to her because she can only be impregnated by one man (at a time), so more partners does not
mean any additional generations, thus most women have no instinctual attraction to seeing multiple men and thus more readily use knowledge over instinct.
Back on topic: Les Claypool is the man
Why do I overthink these trivial issues?