Why do conservatives run talk radio?

This was explored in detail by Sue Wilson here and it turns out that there are two overriding reasons:

The answer is policy-makers, with campaigns financed by those same corporations, changed two important rules. In 1987, then-President Reagan's FCC got rid of the Fairness Doctrine, which required that radio and TV provide a "reasonable opportunity to hear both sides of controversial issues." The Reagan administration thought the marketplace would provide its own balance.
     Then, in 1996, Congress allowed a few companies to own unlimited numbers of radio stations. Huge conglomerates bought the best and biggest stations, and purchased multiple stations within the same market. Then they blanketed more than 1,700 stations with conservative talk. Using their newly created economies of scale, they offered businesses special packages to advertise on stations they owned both locally and nationally.