This is actually VERY IMPORTANT knowledge. Knowing how much your body can take and knowing how to fall in a way that increases how much your body can take could mean the difference between life and death in many situations.
As the Grim Reaper said when asked about giving a sword to a kid who could cut themselves: "That will be an important lesson."
Six-year-old me was fascinated with jumping off of the thing. And yes, it hurt sometimes. I fell on my face, I fell on my ass, I took hard landings that jarred my bones. But I learned, and it got to the point where I was taking a running start before jumping off (Parents pulled the plug at that point).
Kids should learn that sort of stuff. Ideally, you want to protect them from "kill / maim you with no warning" stuff like electrical transformers, the third rail on the subway, dangerous chemicals, etc. You want to inculcate a healthy fear of stuff that will cause lasting harm. And, well, everything else should be free game. My parents told me I was free to go wherever on the bike as long as I stayed away from the really busy roads and wore my helmet (again, kill / maim you with no warning).
The funny thing, to me, is that many of the sports that kids play are far, far more dangerous than these childhood games. Football kills and cripples kids every single year, but it's organized, so it's okay!
Liability and blame. Parents are okay with letting their kids get injured if there is somebody to blame. Like the coach. Or some higher purpose "Oh they were training for a competition"
But parents, and people in general, balk at personal responsibility.