But the bias charge would ring false if everybody was using the same fact checkers.
Think of it as a single agency that syndicates its services to the networks, like an AP or Reuters. Because its reliability is its brand, it would strive to be a stringently factual as possible.
Like a Good Housekeeping seal or Underwriter's Labs.
It accomplishes a secondary purpose: networks that won't subscribe to its scrutiny can then deal with being discredited.