That's only possible because DEs got together and made freedesktop.org, against the desires of many in their various communities at the time. There's little in the way of "Unix philosophy" built into the various freedesktop conventions. In fact there's a lot of "don't reinvent the wheel" in the conventions which is not really addressed in the "Unix philosophy" which is rife with reinvented wheels.

There's still plenty of GUI tools in the FOSS space that don't heed freedesktop conventions. There's also still people that bitch endlessly about D-Bus, systemd, any anything that's not just piped plain text everywhere.