The org.freedesktop.Flatpak user D-Bus service isn't just used by
flatpak(1) or applications running as Flatpaks. It's also used by
toolbox(1) for similar reasons:
* To keep various configuration files inside the container
synchronized with the host
* To let the container request certain commands to be run on the host
Unfortunately, the utilities other than flatpak-spawn (ie., xdg-email
and xdg-email) that are meant to replace their counterparts in the
xdg-utils package don't work inside Toolbox containers [1]. Moreover,
there are RPM packages out there (eg., google-chrome) that "Require"
xdg-utils. This causes conflicts if flatpak-xdg-utils is installed.
Since Toolbox only needs flatpak-spawn to be present inside a
container, there's no need to pull in the other utilities in the first
place. It's a simple way to step around the above problems.
[1] https://github.com/flatpak/xdg-desktop-portal/pull/348