They simply follow a different pricing strategy than the competition. Steady prices produce an image of higher quality compared to other games that land in the discount bin after a few weeks. Other publishers devaluate their own games by setting low prices. Why should I buy a game full price if I know for sure that it will be much cheaper in a couple of weeks? Other publishers double harm themselves by cutting into their own profits and by deflecting the quality of their own products. Customers nowadays fully expect discounts and to some degree have adapted their purchase behaviours accordingly. It's a negative trend set by the publishers themselves. I understand that the prices can be set by the retail stores, yes, but I also believe that they don't set the prices however they feel like but rather according to an MSRPs which they receive from the publishers.
With Nintendo games, it doesn't matter when a customer buys them because the prices will stay steady. This is the reason why we see many Nintendo games having strong legs. These effects go hand in hand. You buy a Nintendo game when you are ready for it, and I believe that customers will enjoy games more if they truly want to purchase them instead of buying them when they happen to be on sale.
I believe that this publisher habit of decreasing prices shortly after release led us to this high emphasis of first week sales. Back in my days nobody gave a shit about how many units could have been sold within the first week, nowadays it's a key figure. It was all about lifetime sales.
You may agree or disagree with Nintendo's strategy. It's successful, however.