Why does liberal radio fail?

I know atleast some of the liberals here will cite the "vast right wing conspiracy" as the reason liberals can not make it on the air. Well, if people wanted to listen to them, they would be on the air.
You might be able to show a small number of cases where the liberal talk show host had low numbers instead of almost a zero rating, but that doesn't explain why in just about every single market Air America was in, the ratings were terrible, and now it is finished.
Lets see if we can get any honest answers.

Here are a few stories on air America ratings:
ouch

I'll go on Arbitron and show you myself
Detroit: .4 rating 31st place...conservative talk radio...5.6 rating...1st place
Chicago: .3 rating 39th place...Conservative talk radio number one and eight
New York: "air America's flagship station...0.6 rating...33rd place

I could keep doing this all day long. Its obvious the problem is no one wants to listen to it.