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.
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.
The Medes turning up to fire the clay tablets probably contributed a lot to their longevity.
This just isn't an issue at all. You're not taking historical documents off the shelves of a modern building - and if you were, sunlight still wouldn't matter - you're digging them out of the ground. Water is what matters; that's why we have so many things from Egypt that could never have survived anywhere else.
Fire, yes, it's worse for paper than it is for clay. But like I just said, we're missing the majority of Mesopotamian documents because they were never fired. We still have a minority that were. What does the same logic applied to Egypt tell you?
And even what survives today much of it is fragments and are torn and incomplete and has to be carefully handled to avoid further deterioration.
Water is not the only thing that matters. UV is extremely damaging over time. Oxygen is damaging over time. Insects, too can chew apart papyrus.
You are only digging the ones out of the ground that happen to have been kept in careful containers or tombs. You're not going to uproot an old papyrus document that has been buried under 6 feet of earth for 3000 years like a fresh potato. Even the mechanical stress of being shifted and being under pressure around can easily tear it apart and disintegrate it over time.
Anyway I feel that the rumours of fire "destroying" the library of Alexandria are extremely exaggerated, because the monastery on Sinai is extraordinary in its breadth and depth, and nobody's really talking about how all that material got there, except for their patroness, whose name it bears, and who I feel has been essentially a personification/allegory of the Library itself.
Alexandria, as a nexus of documents brought far and wide across the Mediterranean, was clearly instrumental in solidifying and bolstering the doctrines and epistolary literature of the Early Great Church.
Historians say that the "Library" was more of a clearinghouse where every ship in port was raided for its documents and papers, all copied laboriously, and sometimes returned to the captains: sometimes originals, sometimes the copies only. They also took other measures to seek out manuscripts and add them to the local archives. So, Alexandria essentially built its archives the same way that OpenAI has done it today. And I don't personally believe that they were dumb enough to permanently store all that stuff next to the famous lighthouse. Those monks on Sinai have been very, very wise men, (shall we say "super intelligent"?), unchallenged for two thousand years.