Would the volume be much higher than the numbers that are reported by surveys like this one, in which women are asked about it explicitly? If so, why?

Of all the respondents, 20% report sexual harassment of some sort. That’s a very high number. There is no reason to doubt its veracity.

But if 50%+ of all men were like that, you’d expect this number to be way higher.

Studies show that something like 50% of men are like that when they know they won’t be caught. And the number goes way up for men who have consumed alcohol.

That's a start. I'd be most interested to see a reference to one of those studies.

Google is letting me down on that.