>>On a decent hill you can get a regular bike going >60mph.

Yes, I've done this before by riding all the way up a local mountain on a road bike, clad in lycra, then on the way down I went over 60mph. It was terrifying and the physical fitness required to get up there in the first place required months of riding to actually do it. Meanwhile literal kids ride these on pavements, in between people, in cities where pedestrians walk - it's simply not acceptable. And I do own and ride an ebike(limited to 15.5mph) legally.