Comment by mirekrusin

Because it's easy to devops-manage it. Your docker image is built by ci during automated tests and that image is versioned and immutable from that point. It'll appear the same on staging enviornments and production environments. It's easy to deploy it on multiple hosts/clusters, manage upgrades/downgrades etc. Involving docker during development in most cases just adds friction without any benefits. There are cases where you need to work in development with docker, but those are very rare.