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.