It really seems like WoW Classic is pulling the game out of the muck in terms of numbers. Might turn out to be bad for the game in the long run if it enables Blizzard to rest on that 'accomplishment'. WotLK will likely be the last big Classic title for many. I can't realistically see many players who were drawn to the idea of 'Classic' move over to Cata so it would probably result in a playerbase that is spread very thinly across three titles (retail, wotlk, cata).
Up until then they can just release these morbid throwaway expansions without really suffering from it, I guess.