True, good modern paper of the types those monk used lasts about 500 years or so in the typical case. (meaning no fire-flood, both of which were common; and not in a carefully climate controlled area which can add thousands of years). We haven't really improved on paper since then. There is a lot of cheap paper that will fall apart in less than 100 years, but those monks didn't use that.

What digital storage do you have that will last that long? A few CDs would in the ideal case (but most are not that grade). I'm not clear how long SSDs will last. Magnetic tape becomes brittle and single read in about 30 years as we know from history.

The only advantage of digital is IF you care at all it is easy/cheap to copy to something new.

It only seems like we’ve always had them because most people want books from this century. The further back you go the harder it is to find any type of book, even mass produced dime novels, because a lot of them have rotted away.

If you actually want books to last a long time, they must be stored under controlled conditions by an actual archivist.