Well, first off, their IPs are amazing, so it's hard to justify making new ones. Sure, some of us older gamers may crave freshness, but when you consider the fact that a college-aged player's first memories are of the Wii, you can see why Nintendo wouldn't really see the problem.
But yeah. I mean, Zelda, Mario and Metroid were created in the mid-80's. Most of their IP is ancient, great or not. So there is definitely a case, imo. I know I welcome new IP from them, so long as it's up to their standards.