That's not the whole story. Juuls are ultra high resistance devices due to their size. Generally that means they can't vaporize as much liquid into vapor, which means traditional eliquid (lets say 3-9mg/ml) isn't as effective anymore, especially for someone trying to quit smoking.
Going anywhere above 12mg/ml with traditional eliquid production techniques produces a liquid that is very harsh.
So, here are your business requirements: You've got a device that is high resistance. You want high nicotine content because your primary market is ex-cigarette smokers. You can't use traditional eliquid because it would result in a harsh experience, which reduces the probability of cigarette smokers quitting and using your product. So you invent something new.