majority of people have liberal beliefs, polls show that, we all know it. we see it every day on the street.
sure, they call themselves "independent" or "conservative", but the way they answer questions on issues, well... they're liberal.
Therefore, we'll see more liberal coverage, on more liberal networks - because that's what more viewers want.
If the history channel had more fans than the NFL, we'd all be watching WWII constantly. Liberal TV just has more fans.