That’s very carefully handled books.
My kids books are in no shape in a matter of months. Then adults also spill, grease, and tear their books. I had to buy some cheap second hand copies for a series with no digital release and they’re gross, I made them grossier, and they’re going to the trash bin after me (there’s no shortage of them in the world).
My amazon account is outlasting most physical books I bought in these in the last decade (I also hate amazon kindle’s lack of book organization, biting me hard at the number of books I have, but that’s another topic)
PS: for people going through 3~4 books a week, storing books for 50 years is a nightmare.
I have original-run Animorphs books, over 20 years old, from when I was age 8-13, all looking near-new. The pages are a bit yellow from age, but there's otherwise no damage. Same for the rest of my collection (some of which were published earlier, though I think Animorphs might be the oldest-printed ones I have).
The collection my have been careful curated but it was improperly stored. The (onerous) way to "store" them, (in hindsight,) would be to copy each of them would have been to copy them all to 3.25" disk when those came out, then (briefly) to zip disks, then CD-R, DVD-R, Bluray-R, and then also included a drive to read them in this backup, once it became apparent that spinny plastic frisbees were no longer a popular data storage format. Or copied the data to archival LTO tape, going up in number as new standards came out.
Or instead of moving between archival format, the other options is to copy it to hard drive and keep moving to bigger and bigger drives, and have online copies and not offline.
If that all sounds too ridiculous and no sane individual would ever do that: you're right and we hang out on /r/DataHoarders.
They might not be our individual personal copies, but they’re there, actually accessible.
To your point, I am strongly for enforcing DRM clearing after the copyright expires or the entity owning them goes under (it should be required by law IMO). I also think collectively we have a fighting chance to preserve copies as long as they’re free of DRM.
I don't know if they're from 1969 - but I do own a few punch cards...
The point is that it's actually fairly hard to beat acid-free paper for archival storage.
For me this was true ten years ago.
The tides have shifted. Now a physical copy means: it will degrade faster than my devices (think books for children). It will take physical place, we’ll have to find it (I can ping my iPad, not my books). Depending on the country it’s printed, it might not even come to my life, the price will be double, or it will be 3 weeks after the moment I wanted to read it. It wi be in a single place, I can’t share it with my family or even my devices the way I share my amazon account. There’s a physical limit to how many I can keep: floors cracking under the load is a thing of the past.
It’d need a very compelling reason to buy any physical book at this point. I get the tradeoffs, but I had enough time with digital copies to make them work under the best conditions for me, making the upside way higher than the downsides.