Well if they're all paywalled-off that sort of explains why I wouldn't have heard of them. Still a bit weird that apparently they were such a good idea many corporations used them, but none of them had popular Linux/BSD alternatives, even when isolation tech has been in the OSS OS'es for ages.
FreeBSD had the first FOSS alternative with jails, then Solaris with zones. In the intermediate Linux had OpenVZ, but that was a much different container model and required kernel patching.
So if a typical BSD sysadmin would set up a Rails website, would he create one jail for the application server, one jail for the SQL server, then set up firewall rules so that the app server could reach the SQL server and that traffic to the host would be forwarded to the app server?
That may be the real reason. Most people working on server these days may well only have heard about mainframes as something close to myths, much less actually interacted with one in a production environment.
HP-UX vaults were already available in 2000.
One of the reasons of Tru64 existence was to provide a high safety UNIX environment.
Aix had its containers since ages.
I can list many other UNIX and mainframe examples.