Tell me, please, why aren't there more liberal radio talk shows? I first started listening to Hannity and Colmes, but nothing after that?
It's the same reason there aren't more serious news outlets that lean conservative: there aren't big enough audiences to make them commercially viable. Liberal radio talk shows have been tried and failed.
There are plenty of liberal podcasts, including a number of very good ones, but libs and conservatives tend to have different tastes, and those different tastes tend to work better in different media formats. Talk radio tends to favor hosts being able to yammer on for hours. That format tends to be more popular with conservatives, whether the subject matter is politics, sports, or religion. Note that long-form podcasters like Joe Rogan also tend to be more popular with the right.
Libs, OTOH, tend to prefer stuff that requires a bit more journalism and research. If you look up Pew's polling on which media outlets are trusted by each side, libs have a greater preference for print publications and those who do real journalism. But journalism is expensive and time-consuming and doesn't provide enough content to fill out multiple hours of airspace a day. In order to fill that much time, you have to bloviate, a lot. And American libs don't prefer that.
That may sound like I'm making a value judgment about conservatives and their media habits, but I'm not - not quite, anyways.
I actually don't think this is a right-v-left thing so much as a populist-v-technocratic thing. I think it's populists who favor the anti-intellectual bloviating of talk radio and it's technocrats who want to listen to professionals talking about professional things; and in the US, it happens to be the right that skews much more heavily populist. If we had a stronger left-wing populist movement in this country, maybe the media landscape would look different.