I suspect it is mainly because there is no one around who would be in a position to allow redistribution of images.
Which would be the saddest possible reason, in a way - if some company or person sat on the copyright and flat out refused to allow redistribution, there would at least be hope for that person or organization to change their mind. But if there is no one left who could consent, that day will never come.
Of course, if there was no one left who could give permission, that would mean there was no one left who could complain or sue; but ethical issues aside, I would not like taking that risk.
That's not so remarkable, considering that IBM's VM/370 operating system supported virtualization in the early 1970s (you could run various IBM operating systems in a VM/370 virtual machine, including VM/370 itself):
When you count IBM mainframe Unix vendors like Amdahl UTS, Interactive Systems (ISC) VM/IX, Locus Computing AIX/370, etc, Unix virtualisation (under VM) actually dates back to the 1980s, with the earliest iterations of it reaching back into 1970s (early versions of Amdahl UTS c. 1979 and earlier work done at Princeton to port Unix to VM/370 c. 1975-1976). So Cray doing Unix virtualisation in the 1990s wasn't from that perspective particularly novel. Pretty much continuously from the late 1970s through to today, there has been some variant of Unix running under VM somewhere.
Side note: I'm struggling to read these articles with the very thin font used (on MacOS). Using font-weight: 300 with Helvetica Neue is a strange choice that I'm seeing in more and more blogs. Maybe it looks more readable with other OS fonts and is just an oversight.
Bumping it up to 400 in dev tools makes is far more readable.
It seems to be something that does originate from the MacOS world, where apparently that choice does not produce such thin strokes that are so hard to read.
While Dev Tools certianly can fix the brokenness, here is a bookmarklet that will do the same:
Mac user here. I also see thin strokes that are hard to read. I've started just putting my browser into readability mode for everything, which accomplishes a similar result.
Or closing the tab without bothering, if readability mode can't handle it.
