The Forgotten Realms have the double factor of following the five base assumptions of the rulebooks, and hewing to the default Heroic Fantasy genre tropes the rules also assume as the baseline.
If you want to phrase it as "assumed baseline," "vanilla" or "what the writers aim for when making material" it's the same result in the end. And it is notable that the rules aren't the way they are because they use the Forgotten Realms as the baseline, but that during the Next playtest they figured out the baseline most people wanted and found the Forgotten Realms fit like a glove: the popularity of Forgotten Realms material is more with homebrewers who repurpose Forgotten Realms material for their hoe games, because they can use that vanilla base than with hardcore fans.