I think a better framing would be this: people who might be interested in a Wii U may no longer be, because companies like Ubisoft are making it publicly known that their future big AAA games (sans Just Dance, at least) aren't going to be on the Wii U.
This is always Nintendo's problem; expectations. People have come to expect third parties to avoid Nintendo's system for M rated properties -- which, by the way, encompasses virtually every major hit for the big four Western publishers, from Mass Effect to GTA to Assassin's Creed to Call of Duty. By contrast, people expect those games to come to the Xbox, and people buy Xboxes with the expectation that all those games will be out on the system, even if the system flounders notably like the Xbox One has, and even if the games haven't actually been announced yet. The same could be said for Sony; even if the system struggles like the PS3 did, GTA is coming.
Ubisoft's declaration only reinforces those expectations, which in turn makes it even harder to build an audience for those games. Which would be fine, if Ubisoft wasn't releasing one last game of that nature on Wii U. Frankly, I think they decided whatever lost sales might come from the declaration were minimal.