During development of Pikmin 3, Nintendo have realised the increased resources needed to develop new titles in High Definition.
Despite HD gaming being around for more than five years and creeping up to a decade, Nintendo are only just tapping into what will eventually be dated TV output. The jump to Wii U from Wii "requires about twice the human resources than before", confirmed Shigeru Miyamoto whilst talking to investors about Pikmin 3's development period.
Please allow me to explain that we may have underestimated the scale of this change and as a result, the overall software development took more time than originally anticipated just as we tried to polish the software at the completion phase of development. However, we are almost out of this phase, and we are also trying to create something unique utilizing an easier development approach called "Nintendo Web Framework."
With that in mind, future HD projects from Nintendo should arrive at a quicker pace, given the company's continual expansion.