The liberal audience can get all the left leaning talk they want from the evening news. They don't need radio.
The evening news is not honest about what they represent and what their agenda is any more then NPR or PBS. Liberals have always done their best rhetoric through fiction and deceit. Presenting their thoughts and views in the light of day just does not sell.
When it comes right down to it, present day liberalism is a combination of mental laziness and moral cowardice recast as intellectualism and moral superiority. It is an ugly thing for its disciples to share openly.