I'd wager that 14$/month is actually really cheap given who will pay for it.
The average per user may be $5.96, but I imagine that the people who will pay 14 $/month have more disposable income and are therefore in the demographics that advertisers would pay a premium for.
There is a high correlation between people who opt out of ads by paying and folks advertisers want to target. This creates a dilemma which increases ad load on those who don't pay to make up the difference.
The average per user may be $5.96, but I imagine that the people who will pay 14 $/month have more disposable income and are therefore in the demographics that advertisers would pay a premium for.