Several problems are happening at the same time to hurt Talk Radio.
1) The current crop of Talk hosts are aging. Younger listeners don't want to hear the steady diet of non-stop far-right conservative political talk. There's more to talk about than national politics. But because that's what Rush does, and he's been so successful, that's all you hear on Talk Radio, except for Dave Ramsey and Clark Howard doing family financial talk, on some stations.
2) Most Talk Radio stations are on AM. Young people will listen to AM when they have a product that appeals to them. KNBR San Francisco, home of the Giants baseball team, is currently #1 in that market and doing well 25-54. But in most places, there are almost no AM stations scoring any sort of 25-54 numbers. So that's why AM Talk Radio is filled with "You Kids Get Off My Lawn" older Talk programming.
3) Talk Radio does OK in medium and smaller markets, especially where there's no All-News station. Outside the top ten markets, the station that runs Rush also has the largest news team. If you're in Orlando or San Antonio, you almost have to listen to Rush and Hannity if you want top of the hour news, weather and traffic. But in large markets, Talk Radio loses badly to All-News stations.
4) In many large markets, Talk Radio also loses to the NPR station and All-Sports stations. Many of those stations are on FM while Rush and his clones are on AM. Younger people in more urban markets tune to All Things Considered, Morning Edition, Fresh Air, etc. instead of Hannity, Levin, Savage. And young men are getting their non-music programming from Sports stations, with local talk about local teams, plus Dan Patrick and Jim Rome.
5) Talk Radio has failed to produce any hosts of appeal to younger listeners. Even younger Talk hosts like Andy Dean and Rusty Humphries can sometimes talk about topics of interest to younger listeners. But they MUST have exactly the same political opinions as Rush. They might be 20 or more years younger. But because they're on All-Conservative-All-The-Time stations, they have to agree with Rush on nearly everything.
6) The Hot Talk format has failed even worse than conventional Talk Radio. Let's remember there used to be FM Hot Talk stations in many large markets, with Howard Stern as the morning show. When he left terrestrial radio, the Hot Talk format collapsed, with only a few Hot Talk stations, nearly all in Florida, still functioning. In some cases Sports radio has taken their place. But in medium and local markets, you got nothing.
7) There's also the Sunbelt problem. It seems nobody in the Sunbelt wants to listen to any sort of non-music programming on the radio, not Talk Radio, not NPR, not Sports. WSB is #1 in Atlanta but all that's about it. Cities like Houston, Dallas, Miami and Tampa have no non-music station in the top 15!
Yet none of the liberal hosts have been successful.