@ReflectedLight
I have noticed my fully skilled skiing sims often slip/fall at the bottom of the ski slope (the one to the right of the bunny slopes) and put it down to the fact there often appears to be a another non skiing sim stood directly at the bottom of the slope where the ski line comes to an end so I thought they were slipping/fall to avoid these other sims that don't move out of the way for them. I decided to test this out and sent my sim skiing on the same slope in the middle of the night when no other sims were around and while he still slipped occasionally it was a lot less than in the daytime when others sims were milling around. It might not be the same for you it's just something I noticed going on in my game after long hours at the ski slope :)
