It's pretty scary to ride bike/scooter next to cars. Seems like a much better compromise to ride on the sidewalk when uncomfortable than the alternative. There just needs to be some sort of enforcement against ass-holery for those riding.
Pedestrians do not have lanes. When I step around the dog crap in front of me, I could be hit be a scooter operator not giving me enough space for my maneuver.
This is a strange thing to say. It's clearly false, and the alternative (putting them on the road) is clearly less safe.
I do think that the current model where Bird etc allow new users to jump on and go is problematic. It will probably work fine in the future when everybody knows how you are expected to ride them (i.e. full speed on the foot path is not cool), but at the moment things are a bit of a free for all. There's too much excitement when you get on for the first time, and no experienced riders to cool you down.