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.
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.