I think there are a few reasons why there are more transitioning trans women than trans men out there, and on this site.
1.
It's easier for AFAB people to live as gender non-conforming than it is for those AMAB. Society doesn't give a toss about me, who's supposedly female, wearing and presenting male the entire time. The last time I wore female clothes out of choice was two or so years ago, and no one's mentioned a thing. I'm not the only AFAB person who wears male clothing, and presents male. If someone AMAB was to do the same thing in reverse there would be daggers thrown at them when they walked down the street at least, and one of the biggest insults for a man is to be called a "sissy" or similar terms indicating that they aren't masculine enough. Being able to dress and act in a masculine way might be enough for some trans men, and they can live their life as a tomboy without ever having to consider gender/gender roles enough to explore their gender identity.
2.
Trans women are more visible in the media than trans men. The majority of people know that trans women exist, a large percentage of people don't seem to realise that they have male counterparts. Quite frequently I hear the same story from trans men, particularly those who realised they were trans in their teens rather than as a young child, they knew something was right, but until they discovered that trans men existed they didn't know they were trans. If someone didn't know it was possible to be trans then the majority of the time I could imagine that they would just think they're crazy and not mention it to anyone for fear of ridicule.
3.
(N.B.: This part isn't intended to offend anyone, I don't believe that one side has it "better" than the other at all. It's a huge generalisation.) Trans men seem to pass as male easier and quicker than trans women as female, in general. This throws up more problems for trans women in terms of the social aspects of transitioning, so they might be more inclined to stick around for longer, because the issues they face may be on going. If a trans man is passing and stealth then he doesn't need to worry about the social aspect to the same degree, and the questions that would be raised would be more about surgery/packers/binders, and the majority of the time they can be googled. The social aspects of life are going to be harder to find definitive answers on, or the exact same question asked and debated about before.
Of course there could then be genetic things, and AMAB people are more prone to it occurring, but I've never been a biologist.
