Due to Microsoft SQL Server licensing, I would be highly surprised if any Linux distribution were to make it available by default in their repositories.
It's not that the OS supplied versions are outdated. They are updated whenever a minor release comes out.
The thing is, that you must migrate your database between major pgsql releases and you don't want your distro to force it on you. The community pgsql repo has the same rules - you have separate repo for each major release, so no surprises either.