I think that men are perceived as being more kinky than women.
When we see two girls together we think these girls may be just as kinky as we are.
Therefore, it's more exciting.
Also, bisexual men are not accepted by society as much as straight or gay guys.
Therefore, there is more reluctance to admit they like seeing two guys together as well.
I also agree with some of the other reasons presented on this thread.
There are many reasons.
When we see two girls together we think these girls may be just as kinky as we are.
Therefore, it's more exciting.
Also, bisexual men are not accepted by society as much as straight or gay guys.
Therefore, there is more reluctance to admit they like seeing two guys together as well.
I also agree with some of the other reasons presented on this thread.
There are many reasons.