In the real world, I don't think bouncing around generate static to make your opponent paralyze. So why can the move Bounce cause paralysis?
EDIT: include Body Slam too
It most likely to do with Body Slam because they're both fairly similar.
If you were body slammed by anything heavy you would be paralyzed for sure.
Now imagine that from the sky.
I'd assume because it's a mixture of Body Slam and Fly. It gains the Flying type and delayed turn from Fly, and the paralysis from Body Slam.
I mean, that's sort of the tl;dr explanation of it. Bounce is essentially "jumping/hopping as a battling move", using their height from jumping as a more effective but specialized Body Slam.
I mean...it's pretty much a Flying-type Body Slam. So there XD