Nobody normal or sane believes it either so I think they're right not to respond to that one.I mean to be fair I can't imagine any PR person plans ahead for Twitter threads about the Prince of Wales murdering his wife and replacing her with a body double. I'm not sure anyone with any sense would think "yeah, that's a reasonable assumption people will make that we should plan for."
The speculation is being driven by William nearly more than Kate at the moment. If he was acting more like his usual self then there wouldn't be so much speculation.