I think it's a combination of Nintendo as a whole not doing well and Miyamoto being unable to create amazing games due to struggles within Nintendo.
Nintendo does really well at being Nintendo but the last gen really screwed Nintendo up by creating a bubble which popped (a lot of the Wii buyers were one time buyers that never went onto supporting Nintendo or any other console). Nintendo tried to recreate that bubble and failed and was caught between not knowing what to do, do they try harder with the gimmicks, do what Nintendo does or try compete with Sony and MS.
I still believe the last great console Nintendo made was the N64. It wasn't just the console, but the games they brought to the table.
The WiiU has been such a mess for Nintendo, the panic seems to have filleted down to their game development and affected that too leading to the creation of Metroid, Starfox, a delayed Zelda which fans are still waiting on, and only one 3D Mario.
Unlike other peers Miyamoto has such as Carmack, Peter Molyneux, Hideo Kojima etc, he isn't free to develop as he pleases, but is bound by a console, what Nintendo consider to be best for that console and what he must incorporate into the game.







