One reason I can see is the same reason that linuxkit [1] is a really interesting way of putting together Linux OS images: the container ecosystem has produced

One reason I can see is the same reason that linuxkit [1] is a really interesting way of putting together Linux OS images: the container ecosystem has produced some tools that are really useful for building and packaging up Linux userspaces, and being able to reuse those tools in other ways is valuable. With linuxkit you give up some of the niceties of image layer caching, but with an approach like this you get the best of both worlds -- the isolation of VMs but the tooling and usability of containers. [1] https://github.com/linuxkit/linuxkit https://github.com/linuxkit/linuxkit