I would assume that this is part of UA's reaction to losing their lawsuit against Skiplagged. It was obviously a painful loss for them, especially being that practically every news agency covered the story, and they think that they will be able to fight it by cracking down on it. (Well, let's see who wins)
Besides, I believe that UA is probably the biggest victim of HC. At least whenever I'm looking for a hidden city, my best results usually come up with United (especially NYC - TLV).