I just read Louise Perry's The Case Against The Sexual Revolution which is about, more than anything, the asymmetry between men and women in heterosexuality. Particularly, two major things are: the desire for causal sex, and the threshold for sexual disgust. Men are consistently and cross-culturally higher in desire for causal sex, and lower in the threshold for sexual disgust. (Although arousal lowers the threshold for sexual disgust in everyone. Like, someone else getting their spit on you is normally gross. But when people are turned on, this can be overlooked.)

I'm not sure what features of physiology cause this, but if hormone levels are a central factor... then I could see how a bisexual woman with her natural hormones might find it easier to find commandability with another woman, and then if she goes on T an her sex drive changes, then she might find men more sexually compatible to her. I think this is more or less what detransitioner and bi woman Sinead Watson describes happening to her: T cranked up her sex drive and she was super horny all the time, and it awakened her dormant bisexuality. Although she doesn't say she's only into men now: she says she's bi. Which sounds like a very normal-person take on it, and adds to my idea that people who don't are saying so because they have a yaoi fetish or something.