I feel like they've kind of painted themselves into the corner with the way they develop content on this extremely predictable set of cycles.

The dungeons are only one part of their interlocking gear and content patterns and can't just be made better on their own. It would probably be for the best if they completely overhauled the entire system of dungeons, tomestones, and raids, yet they've reached a comfortable point where everyone is fine with it and expects more of the same. If they did redo everything at a suitable point like after another expansion, they risk implementing a worse one than the one they have now, so instead they just continue on and every once in a while reduce the dungeons to try something new.