I guess it's basically a move to push hardware sales. They want the 3DS to be their main handheld for as long as possible (because right now they need to concentrate their software efforts on the Wii U and thus can't release a new handheld) so they decided to go with a redesigned model.
I don't get this talk about the "new" 3DS being their next gen handheld, though. I guess the name is confusing but really, it's just a redesigned 3DS with slightly faster internals. The DSi was also faster and had more RAM (and cameras, a bigger screen, an exclusive eShop with hundreds of DSi-only games, a new UI and a music player) so that was way closer to being a "new" handheld but nobody even considered it to be "next gen". I guess the name really is confusing a bit. The timing for this redesign is perfect for a late 2016 release of their actual next handheld.
Edit: Does anyone know if the screens are actually "better" on this model? As in better contrast and colors and brighter screen? Some sources say the screen is better but then only talk about the 3D.
