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The Wii U wasn't designed for third parties.
No third party asked for another PS3/360 level machine to be their go to console for the next 5-6 years, after already sapping that market for the last seven years. No third party asked for that game pad either.
That would be like saying third parties for clamouring for another SNES level system by the late 1990s.
The Wii U as a hardware system was yet again designed for Nintendo's own needs. They are the ones who over fetishize the concept of a tiny home console and lower electricity consumption, no one else cares. But the entire hardware itself is basically hamstrung by those restrictions and probably made more expensive as a result because it requires a lot of R&D to create such a custom, power efficient chip.
If you gave basically any major third party a choice of what the Wii U is versus say "Option 2" which is 3x-4x more powerful but with a Wiimote/nunchaku and Pro Controller and bigger console casing, they'd all choose option 2. The Wii/nunchaku combo still has a fair number of buttons to run any AC/COD/Resident Evil/Final Fantasy/Need For Speed/etc. game and the Pro Controller would also let them bring over their direct control schemes.
