If you consider that many of Nintendo's IPs date back to the NES, it would be burdensome for them to release more that 1-2 per console generation. As it is, some IPs don't even get sequels every generation. Chibi Robo, Pikmin, Star Fox, F-Zero all missed at least one generation, and those are just a fraction of the titles.
As the years go on and people clamor for more original content from Nintendo the list of fans to placate grows. It's kind of a lose-lose scenario for a company that so many people love to mock, regardless of the fact that they are one of the most consistent, hard working developers out there.







