A few days ago, I noticed that the uuid-runtime package wasn't
installed, though libuuid1 was installed (when I installed Debian)
and had "Recommends: uuid-runtime".

FYI, uuid-runtime got pulled due to the rename of libuuid1 to
libuuid1t64.

Note: I installed Debian with debian-12.1.0-amd64-netinst.iso.

Same issue on another machine where I installed Debian/testing using
debian-testing-amd64-netinst.iso on January 5.

I've eventuelly found

https://www.debian.org/releases/stable/amd64/ch06s03.en.html#di-install-base

"For technical reasons packages installed during the installation of
the base system are installed without their “Recommends”. The rule
described above only takes effect after this point in the installation
process."

Then why are recommended packages not listed explicitly?