thats the main issue they don't use LXC but want LXC kind of functionality and re-inventing the wheels with libcontainer. Indeed it would have been better to keep the docker core as small as possible and move LXC driver code as module. Indeed instead of using LXC userspace tools they might have focused on rebuilding the driver using lxc-go. This would have helped LXC project as well and docker team then can focus on incorporating production quality changes from LXC into Docker like unpriviledged containers.

This is really an issue abandoning a production quality LXC 1.0 code and re-writing it from scratch. This is NIH syndrome.