Why do people shovel out parking spots on public streets?

This post made me aware that this is apparently a thing people do, and I'm confused. The street is public property. It's not your job or responsibility to clear it of snow, so why would someone spend an hour doing so?

I'm a Minnesotan, so no stranger to snow (at least in previous years) and I have traveled to many other states, though not nearly as much in winter. But we do have a procedure for clearing our streets within two days of a snowstorm which works fairly well, and I always assumed other cities that get regular snow had something similar. Is this not the case?