Well, it is basically the same ride as Star Tours and that one still draws lines. So, that boils it down to subject matter and perhaps even location. CoP and CBJ were considered major because at the time animatronics was a new and fascinating thing to witness. As years move along, like the space program, robots became the things that drowsiness is made of. It just stopped being exciting or new and then the entertainment factor had to kick in to maintain that spark. All those major shows had their own story line and their own "special" things.
As much as I enjoy CoP, I am still more fascinated by the fact that the entire floor moves around the stages. That was also a thing that no one had ever experienced. And the fact that after almost 50 years in WDW it still works very well. We take so much innovative engineering for granted today. We are all spoiled by people walking on the moon and i-phones that we have lost sight of the level of thought and engineering that had to go into those attractions. Now they are all just Ho-Hum!