I’m not advocating a view of bisexuality as being palatable, I think the fetishization of female bisexuality is repugnant. But that doesn’t change that bisexuality is fetishized and encouraged for male pleasure, whereas male-exclusive lesbianism is stigmatized and discouraged because it can’t be used for male pleasure. Typically from what I’ve found of male fantasies, the element of self-insertion is what’s desirable. It isn’t gynocentric love that’s being fetishized, it’s the disruption and re-orientation of gynocentricity to suit a male voyeur or participant. In short: Guys get off thinking about having sex with lesbians, but guys can’t have sex with lesbians so they get off on thinking they can instigate an attraction to men in lesbians, and possibly have sex with more than one woman at the same time. Like, I’ve never heard a guy express a sentiment anywhere near the ballpark of finding purely gynocentric love and sex attractive. They’re not attracted to the male exclusivity of lesbianism, just the opportunity to disrupt and destroy that male exclusivity.
However, I do agree that bisexuality is only accepted to the extent which it can be divorced from the defiance of heteronormativity. But the primary difference which I’m trying to emphasize is that lesbianism, when recognized as it should be, is never in accordance with heteronormativity to the extent that bisexuality can be made out to be. In an ideal world female bisexuality and lesbianism wouldn’t be fetishized, but for now lesbianism does need to be recognized as a radical rebellion against the heteropatriarchy. It can’t be obscured as bisexuality, lesbians can’t be seen as generic ‘queers’ with fluid sexuality when they’ve asserted otherwise. The problem is what you’ve said yourself, men don’t recognize the male exclusivity of lesbianism- they want lesbians to be bisexual for their own exploitation.
Long story short, men want lesbians to be bisexual and they perceive lesbians as bisexual as a manifestation of their misogynistic wishful thinking so it’s especially important to establish and defend the boundaries of lesbians who choose to distinguish themselves as only exercising gynocentric sexuality to undermine the androcentric heteropatriarchy.