Why are the older pyramids more preserved than the later ones?

I know that the outer limestone casing of the Great Pyramid was actually used centuries later as a quarry and I suspect that is what happened to other pyramids. Those that came along long after the pyramids were built didn't see them as monuments to the departed pharaohs, instead they saw them as a cheap and inexpensive quarry for limestone, and even the granite below if they could get away with it. Why go into a stone quarry and do back breaking labor carving out the stone when it's already been done and can just be carted away. They didn't care what they were disturbing, just so long as they got their stone.