The same way you claim that the rest of the mainstream tv news is liberal.
Ie it isn’t.
These two give greater credence to GOP framing, and more scepticism to Dem ones. That doesn’t inherently make them conservative. It does make them, however, excessively aggressive in appearing neutral.
I mean we live in a world where calling Donald J Trump a liar will get you labeled as liberal. That will get people screaming bias. So that these sources are considered slightly right of center tells you had far they bend over backwards to not appear liberal.
Which means they report news in a neutral way, but from a rightward/ GOP chosen framing.
And really that’s my main irritation, the chart you posted should clearly and definitively kill any nothin that mainstream media is leftward biased. MSNBC isn’t (wasn’t? Don’t follow current ratings) in the same ballpark as the Fox, CBS, NBC’s, ABC’s of the world. And they don’t pretend to be other than they are. While fox pretends they are the true neutrals, and everyone else liberal biased.