I don't understand how you can square the idea that the market will pay good amounts for content with the fact that ads are ubiquitous, not just something found

I don't understand how you can square the idea that the market will pay good amounts for content with the fact that ads are ubiquitous, not just something found on low-quality sites. If ads weren't the best way to make a living, why wouldn't quality publications like Ars Technica just ask people to pay?