I've never understood why jails didn't take off. I guess maybe since linux took off and the bsds didn't, but they're just nice and elegant.
The very first VPS[1] provider, JohnCompanies, was built entirely on jail (and FreeBSD 4.x).
At the peak we had over a thousand FreeBSD jails running for customers all over the world.
In the end, fancy provisioning and fine-grained resource tuning (with products like Virtuozzo) won out. Although JC is still operating and still provides jail-based VPS.
The offsite backup infrastructure that was built for JC customers became a standalone company in 2006 and was named "rsync.net".
[1] The term "VPS" had not been coined in mid-2001 so I made up the term "server instance" which didn't stick.
FreeBSD jails, Solaris Zones, OpenVZ, and Linux LXC were marketed as fundamental building blocks for improved consolidation and/or improved separation of concerns. These technologies could solve all these problems, but fundamentally they were sold as a transparent abstraction. "To end-users, jails operate and feel just like VMs or real hardware" they said.
Docker was different, docker was fundamentally sold as a higher-level product. Docker is not "just like real hardware", docker was a new way to think about deployment, a new way to think about pre-packaged building blocks.
Docker is operationally different.
Separate kernel and OS is ideal for containers, IMO. What was thought to be a plus with BSD I believe turned out to be a weakness.
The BSD community in general is anti-hype, vs. Docker having a for-profit company (dotCloud) behind it. Even it's first version's website looked nice, had a lot of pretty graphics.
It really does more than people think. Now, the following statement doesn't apply to Docker, but I've seen people with great technical understanding seen choosing totally messy toy projects, because they had a well designed website with pretty images and lots of marketing.
I mean to some degree this also works for Docker in the sense that I've seen people having totally wrong expectations on what Docker does.
It's just what good marketing does: Giving people the impression that something is magic.
The BSD communities always had both a strong no-hype stances. They didn't even have cool names, as they have now with bhyve, etc. They also had a strong "keep it simple" mindset, that counters the "there is magic behind it" effect. It is the sysadmin mindset of preferring boringness and no surprises.
The only other bigger open source project I know trying to be boring to some(!) degree is Go. But that only works, because you can always say "it's from Google" if you need to market it.
Of course there are others, but many of them are way less known.
The only other _somewhat_ new software that I can think of that was considered cool without there being a big hype machine and/or a company pushing it from the beginning is Redis. Out of the nowhere, I mean. Of course there is much cool stuff done by people that already have proven to do amazing things.
But I am sure other people can come up with way more.
My only guess is that, like everything, Microsoft beats it for the reasons MS beats anything: legalese.
OpenVZ was popular enough to support the parent company Virtuozzo/Parallels/SWSoft (many name changes over the years) and the commercial Virtuozzo product is still sold: www.virtuozzo.com .
The lack of OpenVZ being accepted into the kernel, is what eventually killed it IMHO. Since the cgroups and other code that underlies Docker/LXC etc. is in every kernel, it was only a matter of time until the default became accepted and then used widely.