It's quite a bit of work to make sure that a project is available on all potentially relevant distros and always up-to-date, so that only works for popular projects, and even for those there are often alternative package sources to get current versions on older releases etc.

Not really.

The problem there is updates: you'll get bugfixes, maybe even backported bugfixes, but in order to get a new version with new features you either have to deal with installing/building from a non-OS-package-manager source, or upgrade your entire OS.