“update” here referring to the version update, eg bullseye to bookworm. hence the title sources.lists because version updates disable all ppas.
Also, because of the “stable” nature of things, instead of a slow trickle of updates, when you finally update the version, you get a flood of updates. Changing from $PACKAGE version 5 to $PACKAGE version 9 very likely has breaking config changes… Avoiding breaking config changes is the entire purpose of a “stable” distro right?
If on arch, you get those breaking changes once a month, a two year release cycle means that the update to the next debian will have 24 breaking changes involved that you get to deal with all at the same time, while accounting for the fact that your /etc/apt/sources.list.d are all disabled.