Actually, something like small world has two advantages over a static show.
1) It's not static. For whatever reason, the sensation of moving through an environment adds value to the attraction. It's also the ability to turn around in your seat and see things all around you. That's not really true of a stage show. A stage show is designed to keep you looking at all of the proper show elements when it wants you to look. Usually, you don't even have to move your head to see them all. And while it is true that CoP does have some brief sensations of motion, it is limited.
2) Small World does, in fact, get a holiday overlay, so it's not always the same show. True, you can do the same with CoP, but the level of complexity compared to small world would require a lot more effort.
As posted here or elsewhere, static AA shows actually don't have such a great track record at Disneyland. Country Bears are gone. Tiki Room is always rumored to be THIS close to shutting down. Lincoln has undergone numerous revisions, and speculation is that this show will not be coming back...
So, we come back to a few major reasons why CoP is a bad choice.
1) Shows simply don't have a long shelf life. That's the main reason Tomorrowland always seems to need redoing.
2) AAs are, what, roughly 40 years old now. Not very Tomorrowland.
3) The story is also lacking in the Tomorrowland department. I think the final scene at WDW is the same one I saw back in 88, and it felt pretty dated even then. It'd be fine if it were installed at the northern end of the proposed Residential Street/Edison Square, where it could serve as a second entrance into Tomorrowland. Otherwise, it just doesn't work..