Honestly what does it matter what they say? Some Nintendo fans would lose their shit no matter what reason they give.
They'd be called incompetent, lazy, stupid etc. by some geniuses on forums anyway, it's just that the reason for that would change from "they can't get their game to run on the Wii U" to "they can't make a game that'd sell on the Wii U."
I can't quite understand how Nintendo fans don't sympathise with third parties even a little. The fact is third party games do not sell well enough, thus it doesn't make sense for them to come to the platform. The industry is not a frigging charity, do they just expect them to spend time developing a sku that won't make them money?! Just because?