Well, the simple answer is this: the Wii was Nintendo's most successful home console ever. You don't have that kind of success and go, "**** that, we should do something totally and completely different". It's easy for forum goers to be armchair analysts and say, "well, of course, the market wasn't there and blah blah", but that's not how it works most of the time. A lot of bad decisions are either calculated risks that flopped, or just bad in retrospect (Nintendo's choice to go with carts over discs for the N64 is a good example of the latter, despite what people may want to tell you).
There's also the fact that is often denied or just not accepted by internet fandom that power really doesn't matter. There's a lot of issues that caused the Wii U to underwhelm, a lot, and I would probably put system power at the lowest on the list. I won't go into a huge amount of details about why, since I'm rather exhausted talking about that particular point, but there were much, much bigger problems, in my mind, to the Wii U's dilemma than power.