Ever since it release in countries like America and Japan Super Mario Odyssey has been seen as the fastest selling game on the Nintendo Switch.  One of the main reasons why Super Mario Odyssey is considered to be one of the fastest selling game for the Nintendo Switch is mainly because the game was released exclusively for that console.

If Super Mario Odyssey was also released for the Wii-U most people would probably just buy the Wii-U version of the game since the console itself is less expensive.  But at the same time the Wii-U is something that many people would probably trade in for the Nintendo Switch in a heartbeat.