That's fair, I was writing imprecisely. The functionality has existed (at least primitively) on Linux for some time, but culturally Linux admins have been more

That's fair, I was writing imprecisely. The functionality has existed (at least primitively) on Linux for some time, but culturally Linux admins have been more drawn to HW level virtualization instead. OS-level virtualization has been a part of the FreeBSD and Solaris cultures for much longer. Another fair argument is that Docker does such a good job at abstracting the configuration and management of OS-level virtualization that it truly changes things. Maybe. But if that's true, it means that Linux admins have ignored this hugely useful technology because it was hidden behind an impenetrable wall of text-based configuration.