The tech behind it. You didn't find any other device, in 2012, which had the streaming tech like the Wii U had. Nearly without any lag you streamed a full game on your Gamepad or a movie. Some games even doubled the image so any lag had been seen much quicker if you would have compared gamepad and tv. So they put all their effort in the streaming tech but in the end it wasn't mindblowing enough to gather any attention.
Yep.
And even the extra space that the Gamepad takes up in the box costs Nintendo money.
I do think Nintendo concluded the Wii U wasn't going to be a winner a few years ago and instead of putting good money after bad, cut all their expenses to the bone while keeping the price static in order to not lose more money on the thing.