They can't, it goes against the company core philosophy. Anybody can program for the iPod, and anybody can program for the DS(with the homebrew libs), but you

They can't, it goes against the company core philosophy. Anybody can program for the iPod, and anybody can program for the DS(with the homebrew libs), but you can't officially do so for the DS without paying huge amounts of money and "proving" that you are a professional(You can't program in your house), and giving a big share of the profits to Nintendo. So developers just go away and the only games you have are those made by Nintendo itself: Zelda, Mario and the like...the same games over and over again.