This may sound like a silly question, but here's my reasoning for it: Each day that goes by, I see more and more third party Vita titles announced for localization, while countless 3DS titles from third parties, some from very big franchises, remain in Japan with no signs of a localization anytime soon.
Let's take this back a bit, back to the Wii. That system saw a great deal of third party support, but the VAST majority of the support provided was in the form of shovelware, with the rest being mostly niche titles. Wii saw tons of "test games" and "experimental games", but third parties refused to provide a decent amount of true support in the form of AAA games. There were exceptions, sure, such as Monster Hunter 3 and Tales of Graces, but for the most part, this seemed to be the case.
Even the DS had a tough time early on, despite being the successor to the GBA, as third parties quickly backed the PSP and pushed hard for that system to succeed. That followed on to Vita, as I stated earlier, with Vita getting a lot of third party support, and third parties being all-too happy to bring over Vita content as opposed to 3DS content, despite Vita selling well under even Wii U levels every month in the West, and under-performing even in Japan, the land of the handhelds.
The Wii U is currently suffering severely from third party neglect, and while I see a lot of people blaming Nintendo, could it simply be that third parties just don't want to support a Nintendo system? Has Nintendo's pre-Iwata history developed so much animosity from third parties that it's unlikely the situation can truly be remedied any time soon?