Don't understand why str8 males watching girl-girl (lesbian) action.
I think some of it plays into the straight male fantasy that the women are so horny and sex starved, they're fucking each other because they can't find a man who will satisfy their needs. In the consumer's fantasy, he would walk into that room and the women engaged in lesbian activity would immediately surrender to him and fuck him senseless, no matter that he's old, bald, fat, and with a tiny dick that won't stay hard.
Porn from twenty years ago and older frequently had subplots like this: Two allegedly straight women would be so sex crazed they ended up in lesbian activity, then some hot stud would discover them and a three-way would ensue. The women were so hungry for cock they did anything the man asked, including things like anal and ass-to-mouth. The man was frequently dominant, telling them what to do and how to satisfy him and, being sex-starved sluts, they did everything he asked and more. Sometimes he would extort sex out of them another time, threatening to tell that he had caught them in lesbian activity.