Why do men hit women?

First, don't pigeonhole all of us. We don't all do that.

Second, what you're talking about is an extremely complex matter. Generally, it's a display of power and control. Underlying causes... there've been whole books written about gender inequality, rape culture, etc.

My opinion of men who do this would be censored on this site, so I won't say it, but I think you can put two and two together.