If one needs to keep a close eye on changes to make sure they can still
be installed even on a years-old OS, the resulting packages can be
placed in a custom repository set up with the instructions at
<URL:https://wiki.debian.org/DebianRepository/Setup>. What am I missing?
yes, it can be done, but it is a lot more work for individual packagers.
- very few clicks to build custom repositories.
- a build environment for each OS, so that it runs "debuild" in the currently patched version of the OS for which the package it built.
It saves people from having to build their own custom repository, and from having to maintain a build environment for all supported OS versions and architectures. on Ubuntu, packages are built for 14.04, 16,04, 18.04, 18.10, 19.04, and I get all those just from clicking one box for each one. I think it also propagates re-building of packages when a build-dependency changes, without my knowledge or interaction. It leverages the ubuntu build-farm for third-party packages.
With debian, it's kind of all or nothing. Etiher you're in Debian, and it gets built on every platform using the build farm, or it's not, so you get no help at all. Launchpad gives a nice middle road that suits us right now, and if something similar were available for debian, it would provide a stepping stone to being in Debian proper.