I don't understand why the big players such as Facebook and Google keeps insisting on using (appeals to) authority as a proxy to truth, when we have rules and systems for critical thinking.

It seems to me that if the claims and stories in question could be re-posed (e.g. as falsifiable, logically coherent statements or arguments) the worst of "fake news" could be weeded out.

The rest (and biases, etc.) would likely have to be left as an exercise for the (critical) reader.