If you are not paying for the product, you are the product.
The internet culture birthed from the early days of the internet "Everything is free", seems to have captured a whole generation who simply have no concept of cost and value.
Vid.me is another start-up that comes to mind: Youtube sucks, has too many ads, and sells your data. We won't have ads, won't sell your data, and will host all your content.
It made it four years before investor cash dried up and they said goodbye.
The truth is that a profit-maximising business will seek revenue opportunities where it can, and if that means selling both services, on a single-instance or subscription basis, and advertising, it will do both.
Advertising-only or advertising-dominated businesses have a strong tendency to degrade faster and far more prolifically than those with mixed-model funding (I still find The Economist's three-legged revenues stool fascinating: subscriptions, advertising, and Economist Intelligence Unit bespoke consulting and research services, each roughly 1/3 of total revenues).
Paying alone, however, is a far-from-sufficient condition.