First of all you're conflating famous/powerful politicians criticizing or disagreeing with news services when I'm talking about private citizens being critical.
If we're talking about private citizens, that might be because you don't know very many liberals, or because you don't pay attention to what they have to say. I don't really know what to tell you if you never hear/see it; that's on you. You can find all kinds of stories of people protesting CNN (Bernie supporters physically protesting during the 2016 election) specifically, liberals on social media criticizing what you would think is liberal media (a lot of people were very critical of coverage of the Covington Catholic drama), and so on and so forth. I can tell you I see people of varying progressive perspectives on this board be critical of CNN and other non-conservative (y'all conservatives seem to think everything that isn't convervative is automatically super liberal somehow?) sources when appropriate.
When you're talking about people in culture, if anything the left is TOO self critical and is eating its own.
Even given all that, there's no equating Fox News and CNN. I'm not saying CNN is bias free, but bias or not it still engages in actual responsible journalism with things like retractions, sources, fact checking and consequences for mistakes/lying.