Re: Not surprising
People are flocking to "containers" as though they are some magical new feature that has only recently become available, but they are no different than BSD jails, Solaris Zones - which themselves are not much more different than a chroot.
With Docker, although you get native performance, you still miss things like memory overcommit and IO management that you get with a VM and so you can get less performance from a single box.
Docker allows you to split up and isolate applications, but if you couldn't run all those applications on a single host without Docker, then you still cannot with Docker. With a VM you have more control over how IO resources are allocated so that all applications can be run with their desired performance profile.