It's ideological. If you look at the Right, you'll see the GOP grudgingly move in the correct direction on an issue (e.g. immigration) when the grass roots raise enough h3!!.
When the Left loses a national election, however, (e.g. 2004 Presidential race), their leadership cries out that America needs to be better educated on their views ("Our message didn't get out" they'll claim).
In other words, change the masses rather than change the views of the Left.
To that end, their willing minions in the news media go to further extremes to manipulate the Public (because the Public is otherwise rejecting the Left's messages).
This has led the news media down a path of diminishing returns...they have to be more and more sensationalistic (e.g. "Karl Rove is a traitor!") to get less and less support.
Drug addicts learn of this cycle the hard way, fast. Politics is slower. Same eventual end for both, though.