I don't think it's as simple as they were all bisexual and only now can they express it.
True innate bisexuality in men is rare. Most bisexual men I know were either victims of CSA when young or came to identify as such due to internet porn/autogynephilia. I have actually witnessed this from both sides. Formerly straight men who never considered themselves bi until falling into certain communities (e.g. femboys) or becoming obsessed with trans porn (if you're interested /r/TGandSissyRecovery is full of mostly "straight" guys explaining this). There's also a surprising amount of gay men on Twitter who arrived to bisexuality from the opposite end, meaning they mostly ID'd as gay until sleeping with pooners and eventually women. There's literal a whole gay fetish called "straight conversion" which is a hilarious inversion of sissy hypno that encourages gay men to sleep with women. This is the "born this way crowd" by the way.
If a person becomes sufficiently degenerate I always assume he or she also becomes bisexual (Guess why 90+% of furries ID as bisexual). From there you continue down the road of degeneracy to even weirder shit like horses and whatnot (see famous bisexual Vaush). It seems porn addiction very often leads to bisexuality or pseudo-bisexuality.
This is why I say these guys are not "born" bisexual in contrast with the way your average gay man is actually "born" gay. They may be born with certain predispositions, but it's an entirely different phenomenon to your run-of-the-mill homosexuality. 99% of people acknowledge this to be true for women. There's a reason 40% of Gen Z girls in the US identify as bisexual but less than 3% of boomer women do. And it's not cause the boomers are closeted. It's social conditioning. It happens with men too, on a smaller scale, and almost always through the autogynephilic pathway for some reason.
"Porn made me gay" sounds like cope for men who can't accept they have faggy tendencies and want to manipulate women into believing they are true and honest straight men who were just going through a phase. If they were straight, they would be able to have fulfilled relationships with women but they can't, they troon out or chase trannies even while being married to women. These men should not be encouraged to traumatize their wives and children by insisting on living a heterosexual lifestyle because they will eventually fail the responsibilities that come with it.
We have seen many examples of this. TenMuses married a woman and he was still simping for F1NN5TER. This is the furthest thing from heterosexual male behavior. Imagine being the wife of someone like this. He says "Honey, I might be jerking off to sissy hypno in your dress/femboys getting fucked in the ass but I can explain." You wouldn't buy that he is just a misguided straight man, you would think he's a faggot beyond repair. F1NN5TER is also too far gone to ever be able to maintain a relationship with a woman. Nothing would stop him from being a tranny. He should stick to dating men and grotesque pornstar troons (men).
You are underestimating the amount of men who want to fuck men and women, it's not that rare. Trannies and their chasers do not behave in a way that is typical for gay men, that is true but they don't act in ways that are typical for heterosexuals either. Porn makes people more degenerate but it can't change their sexual orientation. Straight coomers remain straight coomers. It's not like men who married women but also fucked twinks on the side were unheard of before modernity, think Ancient Greece.
"I want to suck cock but it's not because I like men, it's because of X, Y, Z reason" okay, the fact of the matter is you still want to suck cock. Whatever motivation you come up with is irrelevant. Sexual orientation is defined based on attraction, no one cares whether it was schoolyard bullying, you parents' divorce or browsing TikTok that made you want to fuck trannies.
It is more accurate to call someone who finds both male and female traits attractive bisexual instead of these terms nobody has ever heard of like autogynephilia and spectrasexual. It also absolutely makes more sense than calling them straight or gay. Autogynephilia indicates bisexuality: He is attracted to women and a man who he thinks looks like a woman. Most of the time, they want to be women so they can attract men.