I wonder why you are getting downvoted so much.
I don't know how common bi-men are (probably more than bi erasure makes us believe) but it feels like a least a portion of them are not ready to come out as bi.
> I don't know how common bi-men are (probably more than bi erasure makes us believe)
They're not that common. The literature shows a bimodal straight/gay distribution of homosexual tendency in men and a more Gaussian distribution in women.
The "bi erasure" phenomenon is that if a man is bi, many will believe he's just gay but in denial. Because he may prefer to be seen as straight than gay, he may just let everyone think he's straight. This would reduce how many men appear to be bi in surveys.
Alternatively, I'm gay and even though I grew up in an area of the US which wasn't that homophoboic. I still hated myself for being gay enough that if I had an even slight attraction to women then I would have just killed off the male attraction side to me. If you're bi and grow up in a world where everything tells you that being gay is wrong, then that part of you that is attracted to guys will probably never get explored.
It also may be because of what I observe as 'masculine thinking' vs. 'feminine thinking'. It appears to be drawn biologically from the genetic male sex and 'male brain' vs. genetic female sex and 'female brain'. Natural variations exist in all things, but if you look at what's most common, with biological sex differences (whch feed cultural 'stereotypes'), they still are what they are.
See Robert Green's book "The Laws of Human Nature" (2018) for his take on the following. It's very insightful. (Chapter entitled, "The Law of Gender Rigidity")
'Masculine thinking' prefers to categorise and bifurcate. (Dualism.) I'm a guy and I consider myself having a 'super' 'male' brain in some aspects even more than the average. I find it very hard to multi-task, and I easily hyperfocus.
Male thinking solves problems by breaking things down and focusing on one part of the picture at a time. It's about specialisation.
Female thinking treats things more as a whole, with everything connected. It solves problems by looking at the whole picture at once. It's about multi-tasking.
I now see that 'male thinking' (as opposed to males), such as 'specialisation', dominates modern capitalism and public policy, and often to detriment. Most females at top levels in business at this time in our culture would appear to mostly have this success because they are 'atypically' strong in 'masculine thinking'.
Personally, I think such leadership needs more female thinking. I'm slowly trying to understand it more, as my own starting point. Modern diversity policies that change what's on the outside (how many penises are around the table) don't actually solve the real problems. We're still picking what's taking place on the inside. We need diversity of things far deeper - to embrace and celebrate true 'feminine thinking' - not just what's on the surface.
So anyway, this could help explain why female sexuality is seen to be more 'fluid', on average, than among males. It's not so much how people actually are, as how people see themselves, because of how they tend to be wired. And this is not even factoring in that there is greater cultural stigma around a male being bi vs. a female being bi.
The reason is that bi men round off to gay whereas bi women round off to straight. Bi women are even sought after by straight men so even women who aren't bi will sometimes claim to be, there is really no such equivalence to bi men. This will give the kind of distribution you are talking about especially when done by surveys as this kind of research often is.
They're not that common. The literature shows a bimodal straight/gay distribution of homosexual tendency in men and a more Gaussian distribution in women.