You're not hearing the examples on the radio to begin with. That's part of the point.
I listened to talk radio when WLS had everyone from Don Wade & Roma to Rush to Jay Marvin. WSB had Mike Molloy, Neil Boortz (libertarian) and Clark Howard (finance.) There were still liberals on WABC. John Earling was in mornings at KRMG in Tulsa.
So the point, again, is that liberal hosts can and have succeeded on terrestrial radio. So the thought that suddenly, there are no liberals talented or capable enough to do talk radio in 2020 is extremely unlikely to be the case.
If the point is the format is now "conservative" talk and that's the only feasible format, that's a valid position. But it doesn't change the fact that if your average talk station got a demo from a liberal host - or a moderate one - regardless of talent, they would not be given a shot at the majority of talk stations. Because they have the "wrong" ideology.
One of the best examples I can think of is Brian Joyce at WGOW in Chattanooga. My impression of him is he's a left leaning, but not entirely in with the PC crowd type of guy. When he was put on the air in Atlanta, he tried to moderate his presentation and be less opinionated (it sounded like) to try and fit on a station with often very abrasive hosts from the right - Kimmer, Shannon Burke, etc. They took shots at him on air anyways, and he was less entertaining than he was on WGOW or on Twitter. The show was removed from Atlanta.
Was Joyce non talented? Far from it. He's excellent. But he held back to try and fit into a station where you could be ideologically outrageous on the right, but got called out by the other hosts for even presenting as a moderate. That isn't a level playing field.
Talk radio used to be a format where entertaining people mixed it up. Rush, Boortz, Marvin, all big personalities who could spar with callers and had divergent views. Modern talk radio is, with a few heritage stations excepted, not a place for moderates or liberals of any flavor.
Doesn't make them all talentless hacks who can't do good radio. We know from history they can.