Recently, two things changed. First, the fairness doctrine was repealed. This enabled radio, mostly AM radio, to create a talk format that offered new voices and attracted a large audience. Second, the internet also allowed many new and unregulated news voices to be heard. This included news aggregators such as the Drudge Report and opinion sites such as Instapundit. One thing that these sources have made obvious is the fraudulence of the legacy news media's claim to be "unbiased."
I believe that liberals honestly believe that they can present "unbiased" news. This is because liberals believe that their world view is the only correct world view: no balancing is necessary. Consequently, I expect that their news outlets will continue to claim to be "unbiased" for a long time to come.