For example, ads encourage sharing. With a paid product, you have to gate access. But then there's a sort of implicit conflict between wanting as many consumers as possible, but wanting to get paid. And especially because it's hard to know the quality of digital media without consuming it, it's hard to know whether it's worth paying for. So there's a ton of friction. That barrier to entry stops virality cold, which limits distribution, and also revenue.

There are ways to do ads well. Google is the obvious example. Highly relevant, not particularly distracting, and take advantage of the intentionality of the searcher.

I think ads are a naturally better revenue stream for digital content. Not to say that they can't or won't be abused.