Much less work than messing with Docker, Mesos, Kubernetes, Chef, Puppet, Rkt, Salt, Ansible, cfengine, etcetera... it's much, much simpler to build OS packages and keep the metadata needed to build them under revision control (git, Mercurial, Bitkeeper, ...) And as a bonus, it is designed to plug into the change management process from the ground up, and not as an afterthought. (Deployment automation and configuration management are not enough for complete lifecycle management.)