Isn't it just as much about deployment though? The thing about docker is that deploying your new app basically means stopping your running instance and starting a new one. You actually don't even NEED to stop the current running one if you have something above it that just knows which instances / ports to route traffic to.

I think docker is about ease of deployment. You still use the same server you just run a different command. As opposed to creating a new image and spinning up said image.

You can imagine roll back / migration is pretty easy in this case.