I suspect it's because many harbor a secret fear that one day they could be accused themselves and they have a deep subconscious fear of females being so unpredictable and vengeful. Many, probably even most, men are uncomfortable about yielding authority and power to others, especially to persons of the 'opposite' gender, or 'weird' sexual preferences.Sadly it does happen. There was a semi recent case of rape allegations against a college student (I think) in the US who committed suicide as a result, and the alleged victim came out some time after and admitted to making it up. Although I think that was more personal than for gain, I don't follow criminal law closely so stand to be corrected.
But yeah it's unbelievably rare. The incels of the internet seem to think false rape allegations are happening every weekend for some reason.
Let's face it, this discussion always has a subtext of: I'm allowed to touch you and if you object, well, no harm done, I thought you wanted it and were enjoying it. No offence (indeed).