But why stop there?

Is an Oath of the Ancients Paladin not basically a nature cleric?

Is a Ranger not basically a circle of the land druid?

Why have one concept in multiple forms?

I imagine a beast master ranger, a druid, a nature cleric and oath of the ancients paladin would not have the same backstory. It works when you simplify them to bare bone tags, but it falls apart when attempting roleplay... or introducing "subclasses of a subclass".