the scavengers like raccoon or stray dog would dig up the body... and then rest will join the crowd. dead/decaying bodies generate pungent smell and attract maggots/flies/rats/scavengers/fleas/lice, etc. which can lead to spreading disease. It can contaminate source of water if nearby.
that's why the proper burial process should be several feet deep, away from water source and preferably next giant tree in a forest to speed up the decaying process. When I was young, I had a large backyard. My dog was killed by a car. My dad buried her next to tree in the forest in our backyard. There was no problem such as scavenger digging it up or any pungent odor. My dad was a country boy from a small village so he knew what to do.
I never really thought about it, I wonder if it was problems in the old days with just a plan pine box?
Thanks, Jiro