The Dry Air Preserved Them
The best-preserved ancient relics in the world come from dry climates, where the aridity prevents artifacts from decomposing. Ancient Sumer had a civilization that might have been at least as developed as Ancient Egypt’s. However, we have more Egyptian artifacts (and therefore a better understanding of Egyptian history) because the desert preserved more.
The air around the Dead Sea is sweltering and dry, due to the high salt content of the Dead Sea and the fact that the Dead Sea basin is the lowest land place in the world. The Dead Sea scrolls were not perfectly preserved, but many of the fragments are readable.