I think the silence in general is a big issue for everyone, not just developers. As for specific problems with the SDK, I think I've come up with a good illustrative example of what LCGeek means when she says the SDK tools are lacking:
Think about Mario Kart 8. That game was hailed for its spectacular lighting work, and having a game like that running on the Wii U shows that it's quite possible to get very good visuals if you know your way around the hardware. Imagine now that you are a third party developer, and you received a SDK from Nintendo with barely any content examples or adequate tools for developing said lighting, and then you see MK8 release, and know that it was done internally by Nintendo.
When you see that, it must feel like a sucker punch to the gut. Nintendo knows how to program these visuals on a Wii U, yet they don't give you any input on how it's done. It honestly feels like Nintendo is purposefully holding back what you can do with the console so that their content, alone, feels like the superior, best showcase on the console.
This seems to be how they treat third party developers, and after many years of this it's gotta be very hard to have interest in developing for Nintendo hardware, when they consistently fail to deliver on tools for you to make your games. Nintendo should have invested time into making incredible tools, engines, tech demos, and examples for the SDKs to minimize the time, effort and money needed by third parties to create games for their console. The fact that they seemingly still haven't done that is pretty worrying for me, much more worrying than any discussion about specs is.