Because if you don't own it, you don't feel responsible for it. That's what makes people feel they can throw whatever they want down a commode somewhere else. Very busy, Christmas is piling up everywhere, and I get to spend the afternoon plunging. Whatever was in the pipe didn't block it all the way, so it was moving from toilet to toilet. Get one draining, and another would back up. Got the bucket and filled every toilet with water in the hopes that the pressure would force the object on it's way. Fail. Grabbed everyone, put a plunger in his or her hand and told them to pick their toilet. "All together now! One, two three, plunge! One, two, three, plunge!"
That didn't work either. In fact, water started spouting from the floor drain. Nothing to do now but wait until Monday, call HQ and ask them to call a plumber, wait for the plumber to come out, plumber has to give corporate an estimate, corporate has to give permission to repair...
I could have stayed and plunged some more, but it's not my toilet.
Was going to take a picture, but figured describing it was gross enough.