a) most cities have few, if any protected bike lanes (or equivalent)
b) scooter riders experience more danger from cars in the road than pedestrians do from scooters on the sidewalk (just think if you'd rather be hit by a scooter while walking or by a car while scooter-ing)
Thus, forcing scooters off the sidewalk is a net negative for safety, is it not?
Electric bikes and scooters really change the game, you no longer have to be in great shape or sweaty in order to avoid taking a car to your destination. Really, safety is the main concern many people have.
I'd agree with you if 1 scooter = 1 less car, that would be awesome. But it's pretty obvious when you visit Paris that it's not the case though, scooters are mainly used teenagers and tourists, who wouldn't use car in the first place.