How do public television stations, like PBS, try to overcome the free rider problem?

In the clarification section elsewhere here, the description including its query given is outlined.

Explanation:

Private networks are effectively removing the business of public broadcasting. There are several other explanations for this, but maybe there is a strong company that popular channels would like to do. They had to prepare their shows in a manner that would draw more fans and audiences. Otherwise, it would be impossible for them to succeed in the marketplace.