I remember the Wii hitting a brick wall after year 3, but it's still amazing just how quickly the system died off. Such an incredible first 4 years, just didn't have the longevity to compete with the refreshed Xbox 360 and PS3 after 2009.
True, the Wii had the best 1st and 2nd fiscal year of any home or handheld console ever with 18.61m & 25.95m respectively and even its 3rd year it manged over 20m, I remember it trouncing the XB360 & PS3 every week in Sales. Hard to believe that in the end it only outsold PS3 by 14m due to the Playstation consoles having a very strong tail.
The switch is the first videogame Nintendo has had to deal with one platform at a time since the NES.
Four pipelines for a dev focus in sell first-party software may be the one reason Wii hitting a brick wall
The other maybe it is the last game direction, likewise Skyward Sword and Other M.