Comment by bluGill

The vast majority of written works did not survive. Paper will rot, and inks fade - in the typical case you only get a couple hundred years (deserts like Egypt give you thousands - which is why archaeology is so interested in Egypt, there is a lot more remaining to study but we have no idea how Egypt reflects people elsewhere). Before the printing press, books had to be copied by hand each copy separately - this is a lot of labor. I'm told (I can't find prices online, just contact us...) that you can buy a hand copied of the Torah (first 5 books of the bible) for prices starting at $50,000, and if you want a known scribes' work the cost can go up to $200,000 - this is a bit of an outlier as the Torah is a sacred work and so they will start over if there is even one mistake (not cross out the mistake), but still that gives you the idea of why you would choose not to copy a book if it wasn't extremely important.

Many of the written works we have remain because Christian monks choose to copy it again and again - we mostly have no idea what works they choose not to copy (there is evidence they choose not to copy some works, but you have to be careful as there were multiple monasteries and one choose not to copy something doesn't mean a different didn't copy it thus it survives anyway). We also don't know which works don't survive because some per-christian civilization didn't copy it - folklore tries to blame Christians but many things didn't survive for them to make a choice. (in other parts of the world it wasn't Christians of course, but same considerations applied to them)