To be fair, y'all had some serious vulnerabilities, including zone escapes and arbitrary kernel memory reads, discovered by @benmmurphy.

To this, all I can say is that I spent from 2005-2014, and then from 2016-2020, doing nothing but security evaluations of products, probably about 60% of which were serverside multitenant SAAS systems of one form or another, and I don't remember ever evaluating (or overseeing the evaluation of) a system that relied on Jails or Zones. Lots of Docker! And, until a few years ago, multitenant Docker isolation was an infamous joke! I'm not sticking up for it!

You can look at the recent history of Linux kernel LPEs --- there has been sort of a renaissance because of mobile devices --- and count all the ways any shared-kernel multitenant system would have broken down. At the end of the day, it's not so much about predicting whether your system can get owned up (it can), so much as: "what do I need to do when there is a kernel LPE announced on my platform". If you're doing shared-kernel isolation, the right answer to that question is usually "fire drill". It's not a noodley thought-leadership kind of question; it's a simple, practical concern.

There were also tons of providers who trusted Linux containers for VPS hosting.

And needless to say it became a billion dollar business, with a great product.

Security requirements (and awareness) have increased over the years, have they not?

gVisor isn't a shared-kernel multitenant system; it's essentially kernel emulation. It's a much stronger design.

In fairness, that's an attack class that's very difficult to eradicate even with virtualization.