Linux

For one thing, image based distros are very convenient. If you tell someone "Just install Bazzite", they will probably have a nice gaming experience without any tinkering, because everything is already set up for you ootb.

You have to understand the concept first. Fedora Atomic/ image based distros are built from top to bottom, not on the same level. If something changes from "above", your install will change too, to an 1:1 copy basically.
Problem is, if stock Fedora isn't allowed to ship/ doesn't have some things pre-installed, it's harder to iron out on the user level, e.g. by negatively affecting update times.

uBlue is basically a "build script", that takes the upstream image, modifies it, and redistributes that with the changes included.
In that way, the image from other users is the same as yours, with the same bugs.
This makes it more efficient and user friendly.

It also allows devs to make their "own" distro with only their changes included, while offering a very solid base they don't have to maintain themselves.

It's a good question.

Fedor does not provide an image for every DE/wm. Anyone can create a custom atomic fedora variant with the desired de.

Moreover, you can create your own image and deploy it to 100 machines and all of them will have the exact same os and packages. This may not be useful for you as an end user directly but the dev who is developing the image for you (e.g. fedora in the case of silverblue) knows that you have the exact same comouter as him and if it doesn't work on your pc, it doesn't work on his, because it is the same. Hence, better support for you.

Yes, all their images are purposefully normal fedora atomic images with stuff tacked on top. Some of that stuff comes in just scripts to make management a bit easier, some of it comes in the form of utilities like distrobox. They also come with zfs or proprietary Nvidia drivers or other things so you don’t have to manage them yourself, alongside tailscale and rpmfusion for nonfree stuff (like codecs). Some of them also have some light configurations, some of them have heavier configurations (especially in the case of bazzite).

You can totally do everything ublue does from a stock Fedora atomic image. Ublue just makes it a little more convenient. A sort of “oh, well I was going to do that anyway”.

Here’s the base dockerfile. As you can see, it confirms all of the above.

Starting to write about this, it is actually really complex as rpm-ostree is really powerful. Read the man entry, it tells a lot.

Ostree can use ostree remotes (like git repos) or "ostree native containers" i.e. OCI containers (like Docker, Podman etc. which uBlue uses.

the rpm part meanwhile allows to add any RPM to the image, but it takes way longer. So doing this centrally is more efficient.

This has tons of benefits like adding packages that Fedora cannot legally add, or doing opinionated changes, or unstable stuff like drivers.

Instead of having every user apply them, this does them once and by that increases reproducibility.