Why are old kernel images not removed automatically to free required space on boot partition on Debian?

I do have unattended-upgrades (2.8) installed and the process is running. Yet it frequently happens that I get this error when trying to install upgrades: Processing triggers for initramfs-tools (0.140) ... update-initramfs: Generating /boot/initrd.img-5.10.0-18-amd64 pigz: abort: write error on (No space left on device) E: mkinitramfs failure pigz 28 update-initramfs: failed for /boot/initrd.img-5.10.0-18-amd64 with 1. dpkg: error processing package initramfs-tools (--configure): installed initramfs-tools package post-installation script subprocess returned error exit status 1 Errors were encountered while processing: initramfs-tools This can be solved by manually removing old kernel images with the command here . Some background and a solution when removing the kernel images does not work (this happened once) is here and the so far inactive bug report in the completely outdated 1990s style email-based bugtracker for Debian is here . I'm using Debian 11 with KDE. This has been happening for a long time and has occurred many times now. Why is that (or how to find out)? If they aren't removed automatically I think the old kernel images should at least be removed, maybe using the command above, when an upgrade fails due to lack of boot-partition disk space.