Over time, due to increasing alienation under capitalism, more men are seeing women as these inaccessible alien beings that they desperately want so they can prove to the world/themselves how manly they are, but can never have for one reason or another.
So to them, femboys are the next best thing because they're feminine like women, but are men, so therefore more "accessible".
Probably not significantly more than the general population, when you get down to it.
Even in a perfectly sexually liberated society, most people are going to be hetero, and the vast majority will be a 0 or a 1 on the Kinsey scale. Cis people will always be the vast, vast majority as well.