There are a variety of reasons why liberal radio talk show hosts have been unable to gain the mass followings of conservative hosts such as Rush Limbaugh and Sean Hannity. According to media scholar and author Jeffrey Berry, these reasons include demographics and attitudes toward the mainstream media.
First, liberals tend to be much more demographically diverse than conservatives. Thus, they are tuned into a variety of different stations (e.g. Hispanics often listen to Spanish-language radio), whereas conservatives are more likely to turn in to a single talk radio station.
Second, conservatives generally distrust mainstream media outlets such as the New York Times and Washington Post. Thus, they are more likely to turn to conservative talk radio hosts to learn about current events. Liberals have much more trust in the mainstream media. When they do tune in to talk radio, it is usually to public radio programs from NPR or other local stations. For these reasons, it is very difficult for liberal talk radio hosts to gain the following necessary to stay on the air.