Most bicycles do avoid sidewalks, from what I've observed - I've seen many cyclists on the road and few riding on sidewalks.

I don't think there's much point in drawing a distinction between scooters and bicycles. They will have similar traffic considerations and both are a menace on the sidewalk. It'd be great if we could cater to both, but the answer isn't to bring scooters (or cyclists) onto the sidewalks.