Cities regulate the use of public parking spaces, including what can park (e.g. RVs often can't), how long a car can stay, and charge fees for use (via meters and such). In Seattle car share companies like Car2Go are paying about $1700 per year per car [1] for the right to "store them" in public spaces. Cities historically haven't regulated sidewalks as elaborately because it wasn't common for anybody to leave large numbers of valuable things lying around on them. Cities are now trying to catch up, but I'll guess what regulations do exist mostly forbid leaving your business property on them without proper permitting. (For bikes Seattle's implementing a flat annual fee of $250,000 per company, scooters haven't really shown up here yet.)

[1] https://www.seattle.gov/transportation/permits-and-services/...