

At least for the German one, it’s essentially a rebranding of existing open source products packaged/adapted to work as a suite.
For example, for editing documents they are using Collabora online (Libreoffice-based), for chat it’s Matrix, for storage Nextcloud, email & calendar from Ox Cloud, etc.







While it’s true that Debian installation used to make use of a TUI and it did not have a nice GUI “live-CD” installation image for a long time (I think until 2019), Debian installation process included a default DE for way longer than that (2000). And before they did, the installation offered a choice between different window managers (back in the days before well established DE suites were even a thing).
They don’t customize the DE much, but neither does Archlinux which is a very popular distro nowadays (and the installer on that one is arguably even less friendly than Debian used to be).
Personally, I feel it has more to do with how other distros (like Mint, Ubuntu, Knoppix, etc.) have built on the work of Debian to make their own variants that are essentially Debian + extra stuff, making them better recommendations for the average people (if one thinks of those as Debian variants then I wouldn’t say Debian is “left out”). And for the not-so-average people, rolling release style distros (or even things like Nix/Guix) might be more interesting to experiment in.