In economic terms it's less rent seeking and more rent creation. Like, taking advantage of public sidewalk space may not be a rent in the strictest sense given that the revenue model is still people paying for the service, but the ability to provide that service is absolutely predicated on taking over and monopolizing this public resource to the maximal degree possible.
By historical allegory, harkening back to the original destruction of the Commons, we're looking at Enclosure 2: Frisco Drift.
Let's also not lose sight of the fact that those sidewalks aren't a natural formation, and that it's the city government who ultimately takes on the burden of their construction and maintenance. This kind of neo-enclosure of public resources is then another kind of invisible subsidy.

diamondoid. None of the derivatives I can come up with sound anywhere near as dumb as the actual word.