Nintendo doesn't respect the casual market. They view casuals as a cash cow to be milked, and nothing else. One could argue that's true of any market, but the reason why casuals are being preyed on in particular is because it is easy to do so. Its hard to milk core gamers, because core gamers have higher expectations in a game. Core gamers demand good graphics, good quality, and depth, but casuals only play games for 10 minutes a day or whatever so why bother putting a lot of effort into games for them? And it shows. The Wii might not be an HD system, but it is capable of decent graphics nonetheless, but if you only ever played games like Wii Sports or Carnival Games you would never know that.
Why invest $100 million into making a 50 hour long game with amazing graphics for the hardcore crowd, when you can invest $1 million in making some glorified tech demo shovelware for casuals which will probably sell just as much? So Nintendo and companies like EA and Ubisoft have jumped on the casual bandwagon because its the easiest way to make a buck. You don't have to put a lot of money or effort into it to get results.