I don't follow...these things aren't comparable. Cities have developed a common infrastructure over decades to facilitate car ownership and usage in everyday life. While they may do the same with rental bikes and scooters in the future, they have not yet done so.
We also have a rich body of legal literature pertaining to car ownership, storage, usage and property laws. Likewise, we don't yet have those precedents for rental scooters stored on sidewalks. What we do have is a rough patchwork of sidewalk and property laws we can try to extrapolate from. How's that for efficiency?
That you get a kick out of peoples' dissatisfaction about this, for the reason you stated, suggests to me that you don't actually understand why they're upset. I don't think most people are strictly concerned about how literally space-efficient the scooters are; rather that they have a tendency to be parked on a sidewalk. People would get pretty upset if cars were suddenly parked on sidewalks without oversight too.