Newspapers have always held biases, at least editorially, but they've been open and frank about them. Even the Sun generally writes copy bias-free.
The change has come largely on television where networks used to use their news divisions as part of the public trust for taking our spectrum in order to make money (largely off of US fare in a Canadian context). In general, terrestrial networks' news divisions still hold these principals, despite making little of their profits over-the-air anymore (or on news). Enter the rise of cable news and crusading journalism, particularly in the US. As there was never any public trust to be filled, the glory days of even CNN have withered and wandered only to be outdone, ratings-wise at least, by overtly biased MSNBC and Fox News. Americans have essentially become so accustomed to "their network" rooting for "their guy" that traditional journalism is considered even more biased than the super obvious bias of what they are watching. It's why Trump-heads hate CBS News for example. Even though it is far less biased than MSNBC or Fox News, the fact that they aren't championing either the GOP or the Dems confuses them. People choose the news they want to hear and far too often. Social networking allows us to even curate it to our beliefs. This has slipped into Canada even though we don't have direct equivalents of MSNBC and Fox News.
CBC News goes through a lot of that criticism, despite being super aware of getting different voices on the air. One of the reasons that Conservative insiders like the CBC so much (although they don't state it publically) is because it is so easy to get "their voices" on panels, etc. That need to represent all of Canada should shield CBC from a lot of the criticism it receives, but it often does the opposite. As people don't hear them "rooting" for their team, they must be "biased" even though they aren't rooting for any team. And the fact that they are public means they must be in the hands of the Liberals, despite Liberals cutting the corp just as badly as Conservatives historically and despite CBC breaking more Liberal scandals than most other organizations combined.
There's no easy way out of this bind as the people seem to have made their mind up on what they think is biased and what isn't, but I'd argue that the crusading journalism is more on the right than the left (although definitely exists on both sides) and that with all major media companies being part of billion-dollar conglomerates (save pubcasters and non-profits), the bias actually continues to move more to the right which has amplified their voice regarding the "biases" in traditional media, despite being largely untrue.