The idea that cnn or the washington post are "left wing" outlets is factually wrong.
But that doesn't even address a dependent problem of the quantifiablilty of a political ideology. You can't boil a belief into a number; why do we pretend that polotical ideologies fall on a soft numberline? A libertarian may "lean left" on marijuana legalization, but "lean right" on gun control.
Indeed, the left-right dichonomy's inability to house non-linear opinions or ideas leads to a lot of confusion, especially so in journalism. Where does a factual, source based news outlet lie on the spectrum?
Why do you think they aren't left wing? They are certainly not pro-Trump for instance.
But, suddenly, you realise the importance of large media brands and their reputation?