Why?
Because hitting flat qwater from heights would be akin to hitting a fl;at surface at a lower high. If thw water is unstable it's not going to ba flat & is already broken which allows you not to have to break it upon entering it. If you've ever leap from a high spot into flat water your feet will know the difference between rippled water & flat water. It feels solid & sometimes your legs feel as if they've been drive up through your hips. I once went off a quarry from a pretty high spot into flat water & it felt like a telephone was jamed up my ass. It was very painful.

Barry