The meat is gone in no time, and porcupines get the bones... nothing left but a patch of hair in a few weeks/months. And it isn't big game, or large skeletons necessarily - It is more about population. It is not uncommon to come across a deer or an elk carcass - I have seen many in my life.
The reason one doesn't find predator bones is more about statistics. Predators are spread far thinner in the landscape - by an order of magnitude. One is far less likely to stumble upon their carcasses for that reason. They are rare.
“It is more about population.”
That makes sense! I know that the areas where I have seen lots of bones (elk in both cases) had large herds. I guess even porcupines can get full!? I wonder if past a certain age that the bones are no good to eat?