"why do men shave theat hair around thear genitalis?"
Because a lot of women don't want to floss with steel wool when they give BJs.
Or guys for that matter!
They want to look like pre pubescent boys? I have no idea why guy's shave their cocks. Have you ever asked one? If I saw one at the gym I go to , I'd ask.
I shaved my cock hair one time many years ago. Too much trouble to shave it anyway.
I will be perfectly honest. I did this several times over the years because I like being smooth in that area when having sexual activity with another person.