I think that bisexuality is more common among women for a couple of reasons…first, it’s far more accepted both by straight horny men, and more and more by other women who seem to have shifted from social shaming of it to celebrating the adventurous spirit of a woman who tries it.
Second, society conditions both men and women. Part of the social conditioning imposed upon women is competition for men by trying to appear most sexually attractive to them (this isn’t unique to women, but it is more pronounced than among men who are more inclined toward indifference about our appearances relative to male rivals). In order to do this, women must try to put themselves in the place of their male audience to anticipate what they will find most attractive. A lifetime of looking at other women, and trying to see those women and themselves through men’s eyes kind of conditions many toward a sexual appreciation of women. From there it’s not a great stretch to form carnal desires for women.
This obviously is only generalization and every woman is a person, and every person is individual, but a number of bisexual women have agreed with me that this does describe a cultural tendency.