I am using freebsd since version 8 for all my server needs (was using linux, but got repelled by its chaos which I dont care about on my laptop, but it pisses me off on server). Some more points: - bhyve, developed by netapp, they ditched all old technologies support and it works faster on my i5 server than kvm on my i7 laptop. Snapshoting using ZFS is not a feature to discard either. - FIBs, absolute miracle routing…
...except?
Meh. People who want to engage in this argument are generally trying to argue about jails vs. the collection of linux container technologies. That's not Docker. Docker won because of Dockerfiles. Docker isn't, at its core, an interesting container technology. Docker is a simple metaphor and programming environment to leverage container technology to solve practical[1] problems.
And as it happened, it was done on Linux and not jails, owing in large part to the more configurable/toolkit-style/policy-free tools available there. Jails were indeed more mature, but they were solving the wrong problem.
[1] Also thorny, boring problems like configuration management of large apps developed piecewise from components and by large teams. The kind of thing that is historically not well served by the operating system, BSD included.