The only reason Wii Sports (and similar such games) is doing so well is because the masses are complacent and lazy, too weak and/or stupid to go outside and play sports for real, yet they want to feel like they're actually doing something.
Wii Sports isn't a substitute for sports, its a substitute for games. Stuff like Adventure Island and Bonk isn't really being made anymore, at least not in a high profile sense. The big sellers are stuff like Halo, WoW, GTA, etc. These games are extremely time consuming, often violent as hell, and many time impenetrably complex for people who have a life outside of games.
I don't own a Wii, but I'm much more likely to play Wii Sports than I am the latest Final Fantasy or CoD title because these games are f*cking useless in short spurts. Generally I just play stuff like PC Engine or something for DS or PSP.