Reading this makes me wonder what is being done to preserve other, more recent, and less popular systems. If the material relating to Cray-1, probably one of the most iconic computers ever made, has been preserved this poorly I don't have much hope. Old web pages suffer from a similar fate. The fast pace of technological advancement make things difficult but we really should be doing more.
Back in the 70s and early 80s it was like the 'hey day' of alternative hardware and software. There were dozens and dozens of systems, all with their own micro architecture, there are probably a bunch that are completely defunct, even if you had working hardware the software might be extinct. Wang, Kaypro, CDC, there were bunches of them...
The real warning shot this should be to everybody is for your personal media. The video and photos of your family. If you don't actively take part in archiving them (like regularly checking in on them, backing them up, copying them to new media, etc..) it is very possible, some would say likely that in 20, 30, maybe 50 years, you won't even be able to read the stuff. It's already a real chore to play a VHS tape.