They probably just want to make the most money out of their products, but yeah it can be ridiculous at times.

I remember being at a Target not too long ago, and they had a lot of copies of Metroid: Other M for $50.

Because they are 100% playable from DAY 1... Not 6 months from now with extensive patching.

Demand.

• Good working product with value.
• No SAMEY game that comes out 12 months later that competes with prior game.
• Also their games marketing focus is on the game itself NOT on its presentation e.g. the visuals. newGame will be different from oldGame. With third party its usually newGame will look better than oldGame and since alot of their marketing goes into visuals thats a problem. (how do you convince someone to buy the older worse looking outdated game? You dont so you drop the old games price since PRICE is the only factor that can compete with NEW&BETTER)
• Since Nintendo does not drop prices and Nintendo gamers feel no hurry to go and buy the game day1 they are used to buying the game full price even months later. For me it does not matter if I buy a game day1 or 5 months later the price is the same so I do buy it when I feel like doing it. And thats good because this way I dont get a "Fuck I just paid twice as much for that game shit." I simply hate paying more than needed so I love Nintendo's approach.
• Nintendo gamers are more patient. (you just dont have a gaming community that moves from this years to next years game. The games are played for years so NO group/peer pressure)
• also Nintendo games usually are GOTY/Complete editions day1 (thats changing tho which is sad IMO) So you dont have to slash the normal editions price to compete with the DLC crap or editions that include DLC.

This is also why third party has a problem with Nintendo. They suffer from sequelities (compared to Nintendo who bring a sequel to another platform and usually NOT to the same system). Third party games usually lack polish and feel samey therefore they compete with last years game.
Because of that competition they usually drop prices before the new game comes out and again thanks to that alot of people wait for the games to drop in price. Also  because of the marketing hype most of their customers feel they need to have the games day1 or early as possible to be "cool" or be part of the hype/event/launch period. (if you buy Fifa 15 2 weeks before everyone buys Fifa 16 you wont have anyone to play with. So to prevent that from happening you automatically give in and buy the thing)

•  3rd parties expect alot of their sales within the first 3 months and ignore most other sales (because hated BARGAIN hunters and NOT impatient customers)
•  Nintendo gamers feel no need to buy a game early and because of the devaluation due to the price cut just waiting for the game to go down in price which WILL happen is not a big deal for patient people. I do get my third party games that way no matter if PS3 PS4 XBO 360 WiiU 3DS etc. Why would I pay more than needed? and more than the devs/publishers think their product is worth in the end? Third party hates people like me and even tho I buy the games my sold copy does not count since its not in their 3 month time frame".

That and they aren't broken and loaded right up the ass with DLC, day 1 DLC, pre-order DLC, ultra specific game store branded DLC, season passes etc.

I honestly don't mind paying the full price because I know it's a game that's going to work right out the gate and will actually entertain me for hours, I bought AC new elaf knowing full well hwat I was getting into since there were no more decent harvest Moon games of recent dating that I still play New Leaf every single day and have done for a year and 4 months, I can't say I've played any game on my PC for that long, most games are a few days burst to maybe a week and then they go forgotten.

That said I did manage to get Link between words for at least £20 cheaper because I was in the Netherlands last summer and the £ against the Euro was decently strong that I got my money's worth from getting it there at the time than back at home.

Still imagine what it would be like if Nintendo had Steam like sales?, they'd be absolutely insane but I could also see them losing out on good chunks of cash from doing that a lot.

Retailers slash prices if they over anticipate demand and want to move their stock. If a game is basically not selling unless it is on sale than publishers will usually drop the msrp price.

Thats the reason why there are plenty of poorly selling titles that hold their price and plenty of major blockbusters that get sales a few months after release. Nintendo games tend to have very good lifetime verse first week sales ratios and so they usually don't have excessive supply. But theres obviously exceptions.

The wonderful 101 and paper mario sticker star have often had some pretty ridiculous sales for example.

Because Nintendo is associated with very good quality, since the 90's. So everyone is programed to think like that and that's why retailers sell the games at that price. "Oh it's good quality and it's Nintendo, so the price is right" I'm not against that, but sometimes I would like to buy an old game for much less than the original price. :p

Their games are really high quality, and people keep buying them. I just went into Gamestop and sold 5 Wii games for $123 bucks after $14 refurbishing fees. The cashier lady was quite frustrated with that and told me "The only reason why you got that much is because they're all Nintendo games, you know that right?" I wanted to toss her out the window |:(

This.  It's actually a policy born out of their beginnings in the eighties to counteract and prevent the poor business practices of the previous gen.  It's a policy that seems off to some consumers, but now the slashing policies of companies are coming back to bite them as development costs rise and they find themselves forced to lower prices to maintain momentum by consumer expectations that they conditioned.  

Many times it's even the complete opposite, adding more value to those who buy at launch. I've seen retailers competing for launch sales, with prices that won't be matched again for years after.