Why can't you install docker natively in osx?

I would love to be able to use docker outside of Vagrant in OSX. Right now this is not possible. What are the specific reasons causing it not to be limited for linux installations only?

Docker is just an abstraction & automation layer on top of system-provided containers.

The technical limitation is that OS X does not support operating system-level virtualization, like containers in Linux or jails in FreeBSD (even despite the fact that OS X is a half-blood BSD).

But even despite that, Docker aims to provide an easy way to share container images, and to make sure that any Docker image would work on any Docker-compatible system, they had to limit it only to Linux. (That is probably why Docker doesn't support FreeBSD and friends, which do have containers.)

UPDATE: you can use projects like docker-osx or boot2docker to enjoy Docker on your OS X machine almost seamlessly (both create a Linux virtual machine behind the scenes.)