Or some sort of paper. If the practice was not widespread and if there was a worldwide calamity it is easily credible that all their written tests have simply decomposed.
The dead sea scrolls are only 2000 years old, and the only reason we have them is because they were hidden in a cave next to the dead sea. Insulated, arid, and hot.
Paper lasts about 50-200 years without recopying. Copying requires a stability in society that we are assuming was interrupted.
I dunno if it's true, but it's not a stupid or self contradicting thought. They might have written stuff down.
We have cuneiform because they used clay tablets. Basically we have cuneiform on accidemt, because they didn't bother to recycle the clay.