Because you have entire groups of large, well developed muscles to generate rotational force, and you're not doing so in a way that would put unnatural strain on the lumbar spine. we literally rotate our torsos all the time. the external, internal obliques and TVA are very powerful, vascular muscles. You can literally lay on your back and rotate over from a prone position. That's pretty strong.
compare those to your shoulder muscles you use to throw a baseball. In the shoulder girdle, it's your SITS muscles, which all fuging suck. like if you just reach behind your back seat to grab something you can tear one of them. They're poorly vascularized so they don't heal on their own. They were never intended to be strong. They're far more flexible because we evolved to....have flexibility there.
Remember, we evolved from quadrupeds. As we did, our hips got stronger to hold us upright, and our shoulders got weaker and more flexible so we could do things like hold tools and masturbate and drink beer. You don't even have a real shoulder socket; you have a ring of shitty cartilage that just keeps GH joint from flopping around like an asshole. This is called your labrum.
Lastly, back to evolution thing of how we would walk as quadrupeds. There would never be a reason for our foreleg to extend up and forward past midline. So that motion of throwing a baseball or serving a tennis ball flies in the face of millions of years of evolution because we never needed to do it. That's why women can generate very comparable force with a softball; they're using the musculature as it was intended.
This isn't even getting in to how much your body hates holding baseballs and footballs. The forearms were not meant for that at all. That's one of the reasons german grenades had handles; they never played baseball and weren't used to it.
As far as why golfers have so many injuries, it's because (well up until recently) golfers at every level are fat fugs who don't take care of themselves.
tl;dr overhead motions have no place in evolutionary history, all the shoulder muscles are really shitty and can't do much, fat assholes play golf and that's why they get hurt.