Neither us women nor the men are interested in male-male play, but we women regularly engage in Lesbian activities; we women find it physically and emotionally fulfilling, while the men are amused, turned-on, or whatever. Why? I don't know. But in my experience it is common, even among vanilla people who might talk about about extracurricular sexual activities, but never engage in it. In my mind, puzzling sex questions go back to what is evolutionarily beneficial: two women licking each other or finger fucking doesn't waste any reproductive resources (eggs), while guys sucking each other off or whatever dumps sperm somewhere where it isn't going to make a baby. So males with bisexual tendencies are less likely to reproduce and carry on that characteristic, while bisexual women aren't so reproductively disadvantaged.