A sidewalk supports uses it was not built to contain permanently.
People pass, pause, wait, talk, unload, look through windows, manage children, move mobility devices, walk dogs, clear snow, and avoid the objects placed by businesses hoping to make the edge inviting.
The room analogy is useful only if the public floor remains a route. A chair, sign, planter, display, or conversation can enrich the space while narrowing it. The person who can step around the obstruction may not notice the decision made for a wheelchair, stroller, cane, delivery cart, or two people passing.
Storefronts benefit from the sidewalk without owning it. They provide windows, shade at certain hours, doors, light, and reasons to stop. In return, they inherit obligations around clear passage, ice, debris, visibility, and local rules governing temporary objects.
The sidewalk becomes social through repeated brief permissions. A person may stand near a planter without buying anything. A conversation can occur outside a doorway until it blocks entry. Produce can be offered freely if the display does not claim the route needed to reach it.
A shared room has no single host. Its hospitality is measured partly by how many different bodies can continue through it.