I think this is an interesting question, from a biological / psychological point of view... but which can probably have many answers.
One subconscious and less obvious reason might be that, because being gay has been (sadly) condemned and demonized over the course of history, some might consider it thrilling because it has an "out of the ordinary" status. The mind tends to be drawn to unusual things, when they're identified as something that doesn't pose a threat and doesn't need to be avoided. From an evolutionary point of view, it also makes sense for this effect to be stronger in men... since males were usually the ones who went hunting in dangerous areas, so to survive they had to be motivated to venture into the unknown and learn / experience as much as possible. Of course this is a different thing... just saying the base concept might still relate.
Other reasons are harder to think about in depth... especially on a still sensitive mater like this. But for example, males tend to be attracted to female stuff... and lesbians can be perceived as multiplied femininity.
I'm not a psychologist to be clear. But I often wonder about many things, including how the brain works. Some functionality makes sense if you think about it, and add evolution into the mix at times... but yeah.