Well we have a minority of surviving documents from ancient Egypt as well. A tiny tiny subfraction of a percent of that was able to survive and many of them were entombed with mummies and come from higher quality papyrus in general as every precaution of preservation was inherently taken as part of the process.

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.