Ok, now that Disneyland Paris opened Ratatouille, that makes Paris, Hong Kong AND Tokyo (All International) Disney parks with the trackless ride system. Disneyland and Disneyworld STILL don't have one.
I still don't understand why they don't have one, nor have any plans to build one. It's such an awesome piece of technology. Not only that, but the set pieces are usually high quality. I've been on Pooh's Hunny Hunt and Mystic Manor, and both are great rides. If they opened something like this here, i think it would give Radiator Springs Racers a run for its money.
Probably the obvious reason is cost. I know these type of rides are expensive to build and maintain, but c'mon what isn't? Also, aren't the US parks more profitable than Hong Kong or Paris? Isn't that why we pay almost $5 for a churro? Or is it because the international parks receive funding outside Disney? I bet you Shanghai Disneyland will be getting one...
The other reason I see, at least for Disneyland, is space. But hey, if there's a will there's a way they can build it. Disneyworld has no excuse, they've got a bunch of land.