How silly we humans are. If a dead person is exceptionally worthy in our eyes we cover him with a bigger rock than the corpses around him. Graveyards are giant scoring systems, like a morbid version of Hinduism. The better a person you are the bigger a tombstone you get on top of you.
Everyone gravitates to the largest stones -- of course the dead under the largest tombstones are more important than those under small ones). How nice of you to visit your dead ancestors and forefathers. I wonder, would you have respected them that much if they were still alive? A message to posterity: please bury me without a tombstone. If you pay me attention, do it before I die. Same for everyone else. Instead of visiting the dead people you read about, go talk to the people still alive whom you never bothered with.
The bones beneath the big tombstones are only crushed deeper into the ground than the bones under the light ones.