The Wii was very successful. But was very underpowered when compared to the 360 and PS3. As a result it did not get many popular AAA multi-platform games such as Call of Duty, Grand Theft Auto, Assassins Creed, etc.. and when it did get games from those franchises it was a simplified or less feature filled version of the game.
It meant that the Wii was not really viable as your "only" system if you were interested in those games. While the NES, SNES, N64, and Gamecube were either competitive or the leaders technically in their gen.
There's no need to be the tech leader if you're making a great product that people love. The Wii reached out to customers that didn't previously play video games. It was quite amazing.
People who don't know about other franchises, and perhaps don't want the more mature subject matter of the three big franchises you mention, were more than happy with the fun a Wii gave them.
It meant that the Wii was not really viable as your "only" system if you were interested in those games. While the NES, SNES, N64, and Gamecube were either competitive or the leaders technically in their gen.