They are so arrogant they don't even consider their own obvious bias is the reason. Instead, they rely on half-baked studies to "prove" they are not biased and everyone else is wrong. Morons.
"You can fool some of the people all of the time, you can fool all of the people some of the time but you can't fool all of the people all of the time".
Let's face it, stupid will always be with us although some people are will to think for themselves - Thank God.