Actual older than Plan 9 but still alive OSes have done limited and limiting choices but many have something "somewhat equivalent", for instance GNU/Linux cgroups (see FireJail, BubbleWrap etc) or FreeBSD Capsicum. Choosing anything heavyweight is a nonsense.
That's the issue: past IT was made human-centric, the Desktop as the center of the digital World, the humans as someone who bend his/her desktop to his/her needs and desires, with a network to communicate with other humans. Modern IT is "big player centric" and evolve just for their own needs and desires witch happen to be far from all the rest of humans.
Did you remember the big push toward full-stack virtualization (on x86) not so many years ago? Who really need it? In most cases those solutions are just ways to sell hw. Such push turn out to be unsustainable on x86 and so the container era was born, again who need it? Oh, a cloud provider that sell VPS yes, it need both full stack virtualization and various paravirtualization solutions, the rest of the world have no benefit running ks at home, often on a single physical machine. Snap/Flatpack/AppImage? Same story they serve the purpose of giving distro and community independence to commercial players but who need them?
All "modern" IT is prehistoric* respect of original Xerox/Symbolics and even AT&T IT, but sold as new not to improve our life but against our interest giving us just some crumbs and lock-in for the sake of few big players. Those in the FLOSS world who follow the trend are actually workers for free against their own interests.
The demand is "little" just because ignorance is high. And that's a classic in all society, people who know, people with culture, are always a minority, but that's does not means their "desire" are minor, they just know their interest others do not but would benefit equally. And that's why FLOSS should be mandatory and universities MUST be public and well founded to drive the research ahead of the private sector that can only pick some research to implement and sell the outcome not drive the society toward a devastating path.
I think it definitely had its place before containerization but that is when it took off everywhere. It wasn’t a single push it was a years in the making process.