Comment by anal_reactor

The problem with dinner parties is that they only work if all attendees like each other equally. Any group of people talking at once will boil down to the lowest common denominator, so one bad guest can easily ruin the whole event. Meanwhile during a pizza party it's okay to chat in a smaller group, which means that when you have a complex network of "A likes B but doesn't like C who is best friend of B", there's much higher chance of making it possible to somehow divide the guests into sensible subgroups.