57 YO male, straight as a die, currently single and happy.
I’ve had three long term relationships i.e. five years or more, the last one having finished six months ago and I’m absolutely certain now that I’m just not cut out to live with another human being. Whilst I enjoy the companionship and some other aspects of being in a relationship, the truth is I’m actually happier on my own.
Unfortunately by trying to conform to the social norms, in the process I’ve made my ex partners unhappy which I don’t feel good about. Ultimately the relationships have failed because deep down I actually want them to so I can go back to my preferred situation. It’s taken me a long time to realise this which makes me feel stupid and shitty at the same time.
In answer to the OP, obviously there’s no way of knowing but I would guess that some were in the closet but probably more were in that situation for myriad other reasons.