The word premium doesn't have anything to do with the quality of gasoline. It has more to do with the price.
Premium gasoline costs more for two reasons.
It costs more to make. And, there's more profit added to premium by refiners and retailers. But, premium gasoline doesn't cost more because it is better. Premium gasoline has a higher octane rating. If your car doesn't knock or ping on lower octane gasoline, paying for higher octane is a waste of your money.