Actually that's not as true as you think. Liberal political media may have lost the AM radio wars but they are kicking conservativs ass in cyberspace as a media outlet for liberal politics. You only have to look at the success of the Obama campaign which organized it's political message and financing through the internet with a high degree of effectiveness that conservative media failed to match.
It also shows a generational gap. Older, less tech savy people tend to listen to AM radio where as few younger tech savy people even bother to listen to AM radio and gain most of their information. The fact that the tech savy younger generation is trending far more liberal than conservative is a strong indication that conservatives are losing the generational war for the hearts and minds of voters.
In this respect the conservative movement is grossly lossing the media wars. AM radio is a dinosaur and liberal medias success on the internet has demonstrated that conservatives are losing the younger generation by leaps and bounds and have been unable to adapt to changes in media communications. To that affect, the Fairness Doctrine, particularly as applied to the internet, would be of much greater strategic advantage to conservative politicians then it would be to liberal politicians. That is essentially why you see no real serious efforts to revive the Fairness Doctrine by Democrats. It's a political ruse just to get their right wing panties in a wad.
Hell I can't even remember the last time I listend to AM radio and I don't know anyone under 40 who listens to it at all.