The topics are not deleted. When they are locked, they are thrown behind all the other open topics. (which for argonath means dozens of pages back) A standard SMF feature.
As for why this is being done; usually its explained why. In this case people decided to continue attacking each other rather than to give constructive opinions onto the topics at hand.
Indeed. the problems aren't removed in this way and we know that; see it as the opportunity to start the discussion anew, bringing the golden posts from there, back into the new topic for easier overview.
Coincidentally, just like many topics. the problems are spawned forth by the players and have to be fixed by the players. Unless you insist on removing abused features which would mean we'd go to merely a chat script.
TL;DR: Don't take it as censoring or anything resembling that. It's rather to keep the venue clean to prevent an image of the community being full of trolls.