Feel free to disregard this because ultimately its a tangent that doesn't matter; but supermajority is specifically a political term referring to the required threshold to advance legislation when simple majority isn't procedurally enough. It doesn't mean simply a greater share of.a majority

This is how language evolves.

For supermajority: the construction means “beyond majority” or “above majority”, it is implemented as a higher percentage in most systems, and there is a utility in being able to refer to high ratio majority.

So people have repurposed a technical word to a general word, of roughly the same meaning.