I believe the root cause is in
https://salsa.debian.org/ftp-team/dak/-/blob/master/config/debian/dinstall.variables#L25
<<<
# dists for which we import external data (i18n, dep11)
# as thats usually testing and unstable, but we need codenames,
# get em out of the db.
extimportdists=""
if [ "${functionname}" = ftp-master.debian.org ]; then
for suite in testing unstable; do
codename=$(dak admin suite-config get-value ${suite} codename)
extimportdists="${extimportdists} ${codename}"
done
fi
${extimportdists} is later used for iteration in function dep11() in
https://salsa.debian.org/ftp-team/dak/-/blob/master/config/debian/dinstall.functions#L106
so only testing and unstable have updated AppStream-data.
https://blog.tenstral.net/2015/12/appstreamdep-11-fully-supported-in-debian-now.html
and the debian wiki promote otherwise:
The second thing is full DEP-11 support in Debian! This means that you don’t
need to copy metadata around manually, or install extra packages: All you need
to do is to install the appstream package, everything else is done for you, and
the data is kept up to date automatically.
This is made possible by APT 1.1 (thanks to the whole APT team!), some
dedicated support for it in AppStream directly, the work of our Sysadmin team
at Debian, which set up infrastructure to build the metadata automatically, as
well as our FTPMasters team where Joerg helped with the final steps of getting
the metadata into the archive.
