They're probably not pushing Kingdom Hearts merchandise in Disney stores because the average person walking into a Disney store isn't there to buy video games.
That said, I guess I have just one question: why is it such a big deal that 9/10 of Disney fans don't even have a clue what KH is? Disney is such a huge corporation, and their customers span across various demographics. Why is it a concern that Kingdom Hearts isn't a recognizable franchise for all Disney fans? It's a freaking huge success amongst Disney fans who play video games, and that's really all that matters. Why worry about the people who don't play video games? That's like worrying about selling a book to someone who doesn't like to read.