Their platform, their rules.
I run the DD Facebook page. FB's new reach-murdering, soul-shedding algorithm has destroyed the reach of the page. We were reaching as many as 20,000+ per week. Now it's one per cent of that. The point being similar, to clear the way in people's news feeds for the Breitbarts of the world.
A good axiom to remember is, "If the service is 'free,' YOU are the product."