mk8 is good, but it's only a week old. Most people haven't gotten a chance to play it yet. I've been playing it every day since release, but that pattern will stop after a few more days, and I may go to like twice a week. But even that game, some people don't like to play. Also, you can only play it for so long, like an hour or so, then you need to stop it for the day. This is especially true if you are drinking and/or getting high. At some point, you want an even easier game because you are more interested in talking then the actual game.
Game and Wario is a disappointment when compared to WarioWare: Smooth Moves. I really wanted something more like Smooth Moves. Game and Wario is really just a tech demo that they slapped a Wario skin on. I still hope they make a proper WarioWare game. Nevertheless, casual players love the multiplayer modes, especially the pictionary mode. You don't need any video game skills at all, so 100% of people can play it and not feel disadvantaged. This one girl who game to my mario kart launch party, when she saw me next, said she wanted to play the "islands game" again, she didn't say anything about the actual mario kart. Im not even sure if she decided to take a turn at playing mario kart.