How did radio companies such as NBC whos actual broadcasts were free make money?

Advertising: Radio companies generated revenue primarily through advertising. They sold airtime to businesses and organizations that wanted to reach a large audience. Companies would pay radio stations to air their commercials, which would be broadcast during breaks in programming.

Sponsorships: Radio companies also earned money through sponsorships. Companies would pay to sponsor a particular show or program and have their brand mentioned throughout the broadcast.

Licensing: Radio companies could also earn money by licensing their content to other stations or production companies. This allowed other broadcasters to air the company's programs on their own stations.

Merchandising: Some radio companies also sold merchandise related to their programming, such as t-shirts, hats, and mugs.

Syndication: Syndication is the practice of selling the rights to broadcast a particular program to multiple stations or networks. Radio companies could generate revenue by syndicating their popular shows to other stations, which would then pay a fee to air the content.