[rockostrich]

This might be the case for where you live, but I've see dozens of Lime bikes recently around the Boston area (not in Boston proper, but in Cambridge, Somerville, Chelsea, Everett, etc.) that are just on sidewalks. The main problem is that there aren't really a ton of bike racks around. Usually when I bike somewhere, even in Boston proper, I have to search for a bit to find a bike rack. I imagine it's similar for other cities that don't really have the existing bike rack infrastructure.

[Camillo]

Do you mean in the middle of the sidewalk, or to the side, against a wall? The former seems overtly malicious, the latter is a completely normal place to park a bike in cities where people ride bikes.