Conservatives do not completely ignore mainstream news, most of them watch Fox News, which is mainstream. It's the most mainstream of them all. Even liberals watch Fox News.
I always cringe when Fox whines 'main stream media'.
They are bigger than all the others combined.
I think its because they're the only big, right bias media. Cnn, mnbc, nyt, washington post... All are big name and left bias. So its purely count, not size.
It should be noted Fox has probably most conservatives/right wing viewers. The others have to share the left wing/liberal viewers.
I, however, read NPR. Its very center.