The Alien: Isolation Collection is simply a Steam package containing the original game + all DLCs. The SteamDB entry clearly shows that the package contains the Steam app 214490 which is the regular Alien game: https://steamdb.info/sub/79549/apps/
This is not the case for Deponia the complete journey, you only get one steam app and not a bundle of 3 games https://steamdb.info/sub/41317/apps/
And for Metro 2033 redux, it was a complete rewrite of Metro 2033 so it makes sense to have it as a separate Steam app (I still have 4 Metro games in my library)
