So, the answer (also expressed more or less by Alan) is "for some reason".
Really? That's the answer?
If so, why is talk radio invariably right-biased? Is that also explained by "for some reason"?
The same accusation is also frequently aimed at educational institutions. Is academia also biased left "for some reason"?
Well, there are as many left as right cable and radio news programs today. Originally, however, many of the first cable news and talk programs were more conservative. They were responding to the fact the broadcast TV and radio (CBS, NBC, ABC) were democrat and liberal leaning. The most politically influential newspapers, the Washington Post and the NY Times, reflected their sentiment. Except for the rare William Buckley, there were few voices on the right. Cable and radio gave conservatives the opportunity to serve a conservative audience. People like Limbaugh and others who followed him, and then Fox took up the conservative banner. The liberal left stations still own the broadcast airways. So conservative voices have been pretty limited to cable and radio.