I'm a maintainer of the Moby project (which is used to build the Docker Engine), and saw this post got some attention, so let me try to outline some of the changes and motivation. Happy to answer questions if there's any.

First of all, some history; the Docker Engine was a monolith daemon that provided many services; this worked well when using Docker as a standalone solution, but when used as runtime for Kubernetes, this wasn't ideal; many components were not designed for this purpose, which meant they had to be replaced / overridden with hacks to make it work. The containerd project was created to provide a more modular runtime for the container ecosystem, providing separate subcomponents (a containerd runtime, image/content storage) for the container ecosystem to build on. It was created "from scratch" with lessons learned over the Years, providing a modern foundation.

While docker has used containerd as a runtime for many Years, it still used its own implementation for storing images ("graph-drivers"); this implementation started to show its age and had many limitations; graph-drivers have no native support for multi-platform ("multi-arch") images, no support for OCI Artifacts, and no reproducible images when pushing to different registries (among others).

Around 4 Years ago, we started to re-implement the image storage using containerd "snapshotters"; our initial goal was to provide a mostly seamless transition; add multi-arch support, but keep the UX as close as possible to the graph-drivers. Around 2 Years ago, Docker Desktop changed to using the containerd image storage (snapshotters) as a default for new installations, and Docker v29 made it the default for Linux installations.

While we kept most of the UX similar, there are some differences; when storing an image with graph-drivers, docker would pull the OCI image, extract the content (layers), and discard the (compressed) layers. While this reduced storage, it also made images non-reproducible as the image had to be re-constructed when pushing to a registry (which also resulted in slower pushes).

The containerd image storage uses a different design, where a copy of the compressed artifacts are preserved (by default); this requires more storage to keep these extra blobs, but reduces duplication and increases push performance. It was the decision containerd maintainers made early in their design process, and all containerd-based tools have used this model since the start of the containerd project.

We have a couple of roadmap items to improve this in future; some are outlined in this ticket; https://github.com/moby/moby/issues/51581, but there's other options that will become availeble through the containerd image store; support for erofs as an alternative to (tar) compressed image layers, as well as automatic garbage-collection (which would reduce the need for manually pruning content through `docker system prune` (and related commands).

(FWIW; docker still provides graph-drivers as an alternative https://docs.docker.com/engine/storage/drivers/select-storag...)