Coming from a Shacknews interview with Nintendo of America senior director of corporate communications Charlie Scibetta.
"We think we're putting out the right number of Mario games based on what fans are asking for, based on what our own developers' creative visions are. The key to that is as long as there's innovation is occurring within the gameplay, as long as there's new features, then marrying the characters and the IPs that people love is the right call from our standpoint.
If you look at something like Super Mario 3D World, the gameplay on that one that I find really cool is those transparent warp points. Usually you used to go into one and pop out the other, and that was the end of the gameplay experience. Now, there's a whole dynamic there where you can navigate in there, try to avoid enemies, try to get a better advantage. You could theoretically make a whole new game with those kind of gameplay dynamics.
If we didn't put Mario on it, then it would just seem like a new IP. Because there's those new gameplay dynamics like that, we think there's the innovation there that will keep people interested and keep the Mario brand fresh. You could call all the games that we're making here new IP in the sense that they're new gameplay experiences. They just happen to also have the IP that people associate with."