That's true, isn't it? It was one of those features you'd think they would have had figured out, but no.

The idea is that your container image is the thing you want, and is (relatively) immutable, so you delete and create containers when you want things to change. If you need state you can do that with volume mounts, but the idea is that you don't need to 'update' a container, you just replace it with a new one.

That's also what docker compose does, under the hood. It doesn't 'update' a container, it just deletes it and recreates it with the new image and the same settings/name/ports/volumes/etc.

Isn't the ability to do blue/green deployments, canary releases and easy rollbacks huge incentives to use containers?

I think virtually nobody cares about being able to change the image of a container when you can so easily start a new one.