Most people use the word censorship to refer to banning some specific kind of content: banning what. Meanwhile, the discussion around Facebook is usually around how they measure and reward content, not what the content is.
If you're actually being sincere in this discussion, I think you may not see how engagement is just one particular kind of how and it's not a given that social media sites optimize for it. It was an innovation that some sites introduced because it benefited their business model and it caught on for a while. But it wasn't universally adopted, needn't be used at all, and is becoming less fashionable among both sites and users. Facebook's a bit behind the game on restructuring away from it though, possibly because of over-investment and momentum, or possibly because of being a closely-held company that can be philosophically stubborn.