Because where you're clearly drawing a line to get to is "if everyone knows there's bias, what does it matter?"
The problem is beyond bias - it's blatant dishonesty, misleading angles, and outright omissions of relevant information. This information reaches a large segment of people, and while I might be able to say "I can see the bias that goes against my personal opposite leanings," the problem is when it bombards the average citizen with minimal political leanings or interest. That is, quite frankly, the goal of this sort of thing. And the liberals know this, or they wouldn't have orchestrated this 3-year sideshow circus over freaking purchased Facebook ads.