Bisexual men are gay men who want to co-opt a woman for the purposes of raising kids and most straight women will not be interested in that, but will also lie about it when asked, just like bisexual men will lie about not preferring to have a male partner emotionally, if children and outward social acceptability were not important factors to them. https://www.scholars.northwestern.edu/en/publications/sexual-arousal-patterns-of-bisexual-men
There has long been controversy about whether bisexual men are substantially sexually aroused by both sexes. We investigated genital and self-reported sexual arousal to male and female sexual stimuli in 30 heterosexual, 33 bisexual, and 38 homosexual men. In general, bisexual men did not have strong genital arousal to both male and female sexual stimuli. Rather, most bisexual men appeared homosexual with respect to genital arousal, although some appeared heterosexual. In contrast, their subjective sexual arousal did conform to a bisexual pattern. Male bisexuality appears primarily to represent a style of interpreting or reporting sexual arousal rather than a distinct pattern of genital sexual arousal.