This is just speculation on my part so make what you want of it.
Seeing as Nintendo has released a Animal Crossing-game on each console, I truly believe that there were going to be one for the WiiU too. But since the WiiU has been anything but successful and is already considered "dead", the game has probably been moved on to the "NX". The way I see it Amiibo Festival is Nintendos way of saying 'Sorry. You're not gettin ACWiiU. Please have this instead.'
So, what I'm basically saying is that the WiiU is not getting a new Animal Crossing because it's userbase is too low.