While the obvious answer "... because it sells amazingly well at that price" is very true, the Nintendo DS is still one of the least expensive portable electronics devices on the market; and has a massive library of high quality inexpensive games. Realistically, about the only thing I see motivating Nintendo to lower the price of the DS would be if they released a new handheld; which is probably going to happen in the not too distant future, but probably won't be for at least a year.