I remember asking my grandfather about old cars (he was a master mechanic and worked on many of them) and why they were so rare. He said that, at the time, the cars were looked at as junk - unable to perform and hard to maintain. People didn’t want them. So most of them got scrapped.
It’s the same for old computers. At the time that they should be saved, they were looked at as junk - unable to perform and hard to maintain. (One thing to remember was the time when the IBM-PC and compatibles were popular and the #1 feature for a computer was IBM-PC compatibility. All others were look at as non-useful.) So those old computers were junked.
I still kick myself for not picking up my Dad’s C64 and TRS-80 Model 100 when we cleaned out his stuff. He was somewhat of a pack rat, but even he didn’t want to store an old TRS-80 Model 1 or Commodore PET at the time.
As a teacher, he GAVE those old computers away to students who couldn’t afford a computer at home so that they would have something to learn to program on.