You're making the same point that you're replying to. The juiciest users pay, so the non-paying users are the penny pinchers that convert way less on ads, so the ad revenue is obviously very low compared to the revenue from the paid users.
Similar to how people self selected into iOS and android and to this day its way more effective to advertise to less price sensitive iOS users than Android users with cheap phones, though the effect was even larger in the early days.
