> This is why we have lots of Egyptians buildings but not much of their writing and the opposite with the Sumerians.

Well, we have a lot of Mesopotamian writing. Nothing like the amount they wrote, but more than we want to deal with. Most of their writing sank into the water table and dissolved, like the buildings.

Papyrus isn't a reason for any lack of Egyptian writing; just like everything else, papyrus won't rot in Egypt because of the lack of water.

There is enough humidity around the Nile, that is, the places where people actually lived, to rot papyrus. We have some remaining papyrus archives, but those are exceptions, not the rule. There is absolutely nothing like the library of Ashurbanibal.

Papyrus was amazing material for the time, but it was also a curse on future archeologists. The Achaemenid Persians went from being illiterate, to writing on clay, to capturing Egypt and writing on Papyrus, in one human lifetime. We have more surviving Persian writing from the short time they wrote on clay than we have of the two hundred years of their history after that.

UV and oxygen are plenty strong enough to deteriorate paper over time even without water. Never mind the occasional fire as what happened with the Library of Alexandria.