@ seasons
Your guess is right. My system is no standard siduction.
Four years ago I have built my system with antix-17-sid-net.iso as the base.
I have added repos and apt settings from Siduction. Openbox is my window manager.
My system has no pulseaudio and uses sysvinit instead of systemd.
Nice side effect: With iso-snapshot-antix I can create a custom live iso with just a few mouseclicks. So I could build and test the system in VirtualBox and create my install media in VirtualBox. There are no additional apt settings.
Those packages should have been pulled in as dependencies unless you did a minimal install and reconfigured apt not to pull in 'Recommends' packages.
There are dependencies from libasound2-data, but the packages were not pulled in.
On the other hand sound was fine with 5.9 kernel and all linux-image have no dependencies.
So a package would not be pulled in because of a new kernel.
Yes, my system is more or less minimal, but I have not reconfigured apt not to pull in 'Recommends' packages. It makes sense to do so, but in 2018 I did not know much about apt. I am learning this by doing.