Franchises have to be on all platforms even if they don't make a dime. It is about perception and also about keeping those dollars from going somewhere else that then ends up working against them later.
The Wii U version nor similar ports don't need to earn a dime. They spend hundreds of millions just on marketing. Even if all the Wii U version earned was $12 million it is $12 worth of good will, marketing and $12 million a competitor doesn't get.