In terms of physical sales, wouldn't this have more to do with retailers? Nintendo just suggests a price for the retailer. If these retailers have stock they can't seem to get rid of, it would seem that they'd put them on sale as we've seen in the past with major 1st party games being $30-$45.
In terms of Digital, man who the hell knows. But they do put games on sale here and there on the eShop. So while the price drops may not be permanent I do see them digitally and physically at times throughout the year.
Now the actual question, why do I still pay full price for Nintendo games years down the line? Well, I generally trust the quality of Nintendo 1st party titles, I generally know that the entire game will be on the disc/cart and thus it physically holds actual value and isn't a glorified steam key.
As a couple of final notes, though I buy Nintendo 1st party titles at "Full Price" I often don't actually pay the entire thing. Some retailers will take off $5-$10 for a new release so I do take advantage of that when I can.
Also I feel Nintendo's brand name goes a long way. We associate quality with Nintendo because more often than not, they do what they do very well (and have been doing it for longer than its competitors) and when you add in familiarity and nostalgia, all of that feeds into the value of a Nintendo game. As an anecdote when the Wii U launched, I walked into a GameStop and traded in all my 1st Party Wii games (yes, big mistake) to get a Wii U (yes, big mistake) and those games covered the entire cost of the console and then some. The employee made sure to tell me that the only reason I got that much credit was because the games I traded in were Nintendo 1st party games. Even used titles hold great value.
All in all, I don't think there's generally one reason why Nintendo games don't often go on sale compared to its competitors. But to mark it up to "lack of competition" for every Nintendo console doesn't seem right either. Because this question has been asked for decades at this point.







