I wonder, how is it that, despite Persia’s massiveness in terms of size, we have so little original writing from the Persian empire before the hellenistic period (and still less than others afterwards). I personally only know of Avesta as an intact work of literature; what happened to the rest of the mythologies and stories they must’ve championed?
u/Trevor_Culley answers a very similar question here!
https://www.reddit.com/r/AskHistorians/comments/nksole/persian_sources_on_the_achaemenid_empire/
What jumps out at me are two problems: they probably weren't written down to begin with, and if they were they were written on paper-like materials like papyrus which would not have survived very long.
The Greeks used the same materials but a long, long, tradition of prioritizing and recopying certain Greek works (and mind you the overwhelming majority of stuff they wrote is still lost) has led to some surviving to the present day, while many Persian sources didn't receive a similar treatment. But really I think the key is they didn't have a tradition of writing like that, which was in many ways the norm in the region.