My running-theory is that it will remain this way until ghost's OSS version supports multi-tenancy properly: https://github.com/TryGhost/Ghost/issues/1484

Wordpress took off, because you could support multiple sites for various clients with a single-stack - enabling third-parties to run Wordpress-hosting websites easily.

With Ghost, unless you are Ghost.com, you need to run one-container per blog you have, which is ridiculous.