I imagine that similar to how Google keeps its search rankings particulars secret to prevent gaming, they want to avoid being above-board about censorship for s

I imagine that similar to how Google keeps its search rankings particulars secret to prevent gaming, they want to avoid being above-board about censorship for similar reasons. Censorship is not the same as taking a stance on an issue, it is destruction of the discussion itself. If they name what they censor, that will only create more discussion of topics which they have decided it is in their best interests to destroy. They might also be concerned about similar 'gaming' with people pushing what is allowed to be talked about right up to the line without crossing it. This is a valid concern, because I will personally do this as aggressively as I am able given the opportunity.