In this case, serving the market is about scale and no-touch/incredibly-low-touch sales. The companies not charging anything are making money on the backend through data, analytics, and sale of information to 3rd parties. There's definitely money to be made, it just depends on who you are asking for that money from.

Could you elaborate?

It seems to me that $20/year could be a good lowest tier price, especially for products targeting individual customers (as opposed to businesses). There are successful solo founder projects in that range (notably pinboard.in, $22/year).

The company operating on the $20/year model offers a very specific feature-product and that's basically the only thing they do. My goal is to have that be one of the features my company offers eventually and do this with a handful of complimentary feature-companies to build something more robust over time, the idea being that I charge something like $10+/month for a set of "premium features".