It's because non-endogenous testosterone is used to dope. Why anyone would do it in equestrian, I don't know...although anyone who argues riders aren't athletes needs to come take a few lessons. Believe me, it's an athletic *partnership*. The horse does not do all of the work unless you're just going on a quiet trail ride on a packer and even then believe me, you'll be sore afterwards. In places you didn't know you *had* muscles. But there is no advantage for cis men in most equestrian sports. Some rodeo events do advantage larger individuals, which statistically tend to be cis men, but more and more women are being successful in those events now. By which I mostly mean roping, which uses a lot of upper body strength and size. Eventing appears to slightly advantage women, as does endurance riding.

And yes, but the point I was thinking of is that it would mean more to point to cis woman excellence in sports that are typically viewed as advantage men.