In a corporate environment, people want to avoid confrontation even if they are crushing the dreams of the originator. I have no idea if Joe is still working in the company, but this means he isn't in the line of command and he doesn't call the shots.
Part of the reason Harry Potter is so successful is because it taps into those very old myths. Very few new creatures were invented for that world. Most were just picked right out of old stories and used just as they have always been used. A couple were given slightly different spins but wizards learning magic from old books and arcane alchemical processes to fight basilisks and werewolves is nothing new. If someone didn't know what Harry Potter was and you said, "It's about a school for wizards." what pops into their head is going to be close enough to what it actually is.
Avatar has none of that. It's only cultural signifier is white guilt. If you have to explain that world to someone the easiest way to do it is to say, "It's a sci-fi allegory for the horrors of Manifest Destiny." It's longer, clunkier, doesn't really resonate at all within any culture, and with that description, a million people will imagine a million different things. Unless they have actually seen Pandora (itself used by avatar for its cultural significance) they probably aren't going to imagine anything like it.
Creatures of myth and legend are very old. They have deep cultural significance to a wide range of people. In both Europe and Asia tales of dragons go back over a thousand years. 8 years ago there was no such thing as a Na'vi. 50 years ago there was no such thing as a Bantha, but 3000 years ago, China still had dragons.
Everyone knows these creatures. In the medium of a theme park, where there are no voice over intros and no opening crawl to explain the world, you have only your surroundings and maybe a map to determine what the world you have stepped into means. Having cultural signifiers that go back a hundred generations make it much easier. We immediately understand everything about Frontierland because everyone knows exactly what the old west means. Even if it means a hundred different things to a hundred people, they still understand the environment because it is such a big part of our American culture, and that's only about 200 years old. If you show someone a picture of a cyclops, nobody needs to ask you what it is. Everyone's seen it a hundred times before. That six legged horse thing though?