"Everything in the world is about sex. Except sex. Sex is about power." - Oscar Wilde

By having sex with so many men at once, she is giving into a power dynamic that essentially reduces her down to a sexual object. The men themselves aren't important (and in fact aren't really a part of the fantasy at all in some cases). It's their relationship with the woman and how that relationship reflects on any possible relationship we would have with said woman.

In reality we know she is doing it for money, but we can imagine that she is either: A) A girl of incredibly questionable 'morals' and has low standards in a sexual partner, making her both more accessible to us and gives us a feeling of being superior to her. In which case we can easily see her as someone who needs sex and physical stimulation as if it's some kind of addiction. For obvious reasons a woman like this is very attractive from a purely sexual standpoint. If she'll have sex with a room of five strange guys randomly, we can easily see her accepting an invitation from us.

Or

B) The girl is there to serve the men around her. She is not there for her sexual needs, she is there for theirs. She's essentially a living sex toy. Reducing someone to this kind of sub-human level sexually is a pretty common fetish. Again, the real thrill comes from the power dynamic change. It's not considered normal to treat another person this way; in fact it's pretty taboo. The rush of power that comes from knowing you own your partner (at least sexually) is a very strong aphrodisiac to some people. Again, if she's willing to submit to a room of five strange guys randomly, we can see her doing it for us.