I’ve come across many large skeletons in drier climates. Traipsing around in Minnesota or Western Washington - can’t recall ever seeing any. I don’t think it takes long for the bugs and worms to decompose everything.
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.