I think it's because the rules for success are defined by non-Nintendo fans and some weak-spirited Nintendo fans are submitting to it, so they urge others to buy games nobody actually wants in order to earn acceptance by their peers (the internet gaming community). There are plenty of folks out there who refuse to call the Wii a success because Nintendo games sold best on it.
This is so very true. Whether we all want to admit it or not the Nintendo brand has become a niche console. It caters to a specific base of fans and that is it. The way the hardware is developed and the way they position their own software both support this. Hell, the install base is the only reason the Wii got third party support. Does anyone think that third party devs wanted to do HD and non-HD versions of their games?
AAA game development has become too expensive for third party devs to want to cater to a niche group. They would rather focus on the more broadly placed PS4 and XB1. The return on investment for making the games also fit on the Wii U just doesn't make sense to them.
The problem is you have people who own the niche console who also want the more broad experience. They are then forced to either support what comes their way or go get another console for it.