It really has to do with the reputation of their curators for bias, and for promoting their decision.
Facebook is going to stop labeling what they think is fake news, because they noticed that the label is associates with more sharing, not less. Now their hive mind will try to be more subtle, by continuing to bury opposing views, and by planting opposing articles next to the ones they don’t like.
Read Facebook’s own version here, if you want.
Why will Facebook chug along for awhile? It has lefties and boomers (who have the money), to carry it along for awhile. It will slowly die off, as the boomers do. Younger people are moving on. Business people have to hang out for awhile, to keep the boomer customers, but those targeting younger demographics are hitting the road.