Why do Conservatives often bash or say how much mainstream media lies about everything. While FoxNews repeats most right wing talking points?

I often see conservatives blame “mainstream media” for a variety of different reasons with the context being that MSM lies about everything. But at the same time…FoxNews is BY FAR the most mainstream media news source in the country. Their prime time numbers more than double CNN’s viewership.

I guess my question is…isn’t a little weird to say MSM is always lying about Trump when the most mainstream media is for the most part heavily defending him? Like wouldn’t “don’t trust left wing sources” make more sense or is that just not as catchy?