Jails and Zones are kernel mechanisms, they aren't easy any more than cgroups/namespaces are easy (to be fair, yes, they're easier than linux's tools by default

Jails and Zones are kernel mechanisms, they aren't easy any more than cgroups/namespaces are easy (to be fair, yes, they're easier than linux's tools by default, albeit less flexible). What docker changed was absolutely to make things "easy". A Dockerfile is really no more than a shell script, the docker command line is straightforward, the docker registry is filled with good stuff ready for use.