ZombiU, a medium-budget title, actually did fairly well when the Wii U launched, and to this day has over 10% marketshare on the Wii U. That is roughly equivalent to how a lot of sports games have done on the PS4 and One. And of course, you have the Monster Hunter 3 port, which did great for being a port of a years-old game, and LEGO City, which did even better. All three of these games are in the Wii U's top 10. So in short, games not made by Nintendo have a chance on the Wii U.
So let's say Watch Dogs sells 10 million lifetime, including 1 or 2 million on the Wii U. Would that be enough to guarantee a Wii U successor? Especially if Watch Dogs 2 doesn't have a PS360 version?
Third party support was doomed for the Wii U the moment publishers learned that Nintendo would be the guys making it.
This is not to say the Wii U will be entirely barren of third party games. In the near future, Skylanders 4 and Just Dance 2015 will each likely sell over 300,000 copies on the Wii U alone, based on the trends from prior entries in those series on the Wii U. Disney Infinity 2 will likewise likely do well on the Wii U. And of course, LEGO games will do well enough until that fad finally dies.
However, AAA games like CoD and Assassin's Creed won't, simply because people who play these games will likely prefer to play them on another platform. You can blame Nintendo for making a weak console, or possibly 3rd parties for demanding too much power for what are typically not very technically impressive games, but either way, the problem remains.
That said, as a pure consumer, I'm content. The Wii U is not my only gaming device, but even if it were, it would not be a much worse system than the original Wii was. If anything, the Wii U looks to be the Wii with an occasional multiplatform title and a higher quality eShop replacing hundreds of shovelware titles. At very least, I don't groan when viewing Wii U shelves at stores, unlike I did for a while with the Wii's section.