I was thinking about that “Vimes occasionally crawls out of his grave as an angry part-time zombie when someone starts mucking up Ankh-Morpork thing” again and
Patricians get into a habit of doing a ‘state of the city’ address yearly in the cemetery because, well, you’d rather tell him what’s going on than have him come up and check, right? Eventually people forget why that’s the venue; it just is.
People come to the graveside to leave written requests or ask for help. Sometimes they even get it, although not in the way they were expecting. The Watch comes through regularly to pick up all the slips of paper, and they usually have an unobtrusive guard on duty listening. You never know when you might hear something important.
A particularly unpleasant (and short-lived) Patrician attempts to have the coffin chained up. He lives long enough to regret this.