Achivements are not so easily added as people suggest. If you don't track them by means of a database, and you don't have the specific code in your codebase, you need to add it later on, maybe causing all kinds of headaches...

That said, it could be something that is already integrated into Unity, so it MAY be fairly easy to add, who knows?

But then I don't care much either way, since I don't care about a game telling me that I have "achieved" looting 9999 berries during my play time.

Honestly, who gives a f**k?