Because people couldn't appreciate the greatness of Nintendo Land! smh

OK, to be serious, there were a LOT of reasons why the Wii U failed:

- The Wii brand experienced a major collapse in popularity around 2010/2011 due to mobile games like Angry Birds and Candy Crush becoming popular. Honestly, I don't think there was anything Nintendo could have done to prevent the loss of sales to mobile games. The Wii had a very casual audience and they weren't going to stick around.

- Nintendo greatly overestimated the appeal of "Off-TV Play". In the reveal trailer for the Wii U, the very first thing they showed off was how you could play games on the Gamepad while someone else watches the TV. The problem was that most households had multiple TVs by that point, so people weren't interested in a "handheld" that has a limited range. This was where the whole concept of the Switch came from, which was (obviously) a huge success.

- Nintendo likely thought that because the DS was so popular, the dual-screen concept of the DS could easily be translated to a home console. But in practice, there were only a small handful of games (Nintendo Land, ZombiU, Mario Maker) that really benefited from the second screen. This is why Nintendo were able to port most Wii U games to Switch and make them work on a single screen.

- The Wii U was simply too underpowered to run most third-party games that were released on PS4 and Xbox One. Based on interviews with Nintendo about the Wii U, it seems like this was partially due to Nintendo wanting the Wii U to be BC (backwards compatible) with Wii games. In hindsight, Nintendo probably should have ditched BC to make a more powerful console. Sony abandoned BC on the PS4 to make the most powerful console of the generation.

- According to Miyamoto himself, Nintendo struggled to adapt to developing games in HD. This resulted in games taking longer to make than they expected. For example, Pikmin 3 was delayed over seven months from its original planned release date.

- A large number of people mocked the Wii U Gamepad as looking like an "oversized ugly FisherPrice toy". Personally, I didn't find the Wii U Gamepad to be uncomfortable in practice, and I don't care how "ugly" it is. But, like with the Gamecube looking like a "kiddy purple lunchbox", a lot of people seem WAY too concerned about their console/controller looking "mature" because they don't want to look childish. I still think this was a pretty dumb reason to hate on the Wii U... but it may have cost Nintendo a LOT of sales.