1. Because first-party support IS the reason to get a piece of Nintendo hardware. Even Nintendo platforms with either tons of quality third-party games, or just a sheer quantity of them, still are true to this.
2. Because at this point people accept it. They know very few first-party Switch games will go on sale or get a permanent price cut. They wanna play the game and don't want to wait years to get it cheaper. The evergreen nature keeps the price up.

Because they can. You get their hardware to play their games....you think spending full price for Zelda 3 years later is gonna deter people? Of course not. People will grumble that it’s unfair because some games are older then others, but you’ll buy it all the same.

Playstation 4 software sales exceeded 400 million units in January 2017. That's a bit more than 3 years after launch. Almost the same amount of time it took the Switch to do so. Obviously, yearly software sales will increase over the course of a console's lifespan as the install base grows.

Some good reasons have already been mentioned.

To add.

A lot of Nintendo gamers are actual game collectors and take pride in having a nice collection. Go to a second hand section of a game store or even an op shop and what do you see? Countless Sony/Microsoft games and bugger all Nintendo.

Look at past consoles and how many games (especially in PAL regions) have appreciated in value.

The Switch is doing great on Software sales which is sometimes overlooked and is pretty much neck and neck with the PS4.

PS4 hit 401m software sales after 3 year 2 months on the market, Switch is at 406m after 3 years 3 months.

The next number of software sales we know about for the PS4 is 645m after 4 years 2 months on the market which we can compare to the Switch after FYQ1 2022 (end of June 2021) when the Switch has been on the market for 4 years 3 months and I don't think there will be much in it with a slight lead going to the PS4 still but even with a somewhat modest 30% YoY software increase it would total to 218M for FY21 bringing the Switch up to 624m.

I do thinking collectability has an affect actually as myself and plenty I know (yep it's anecdotal) keep all their Nintendo hardware and games whilst constantly trading in the older games on the PS/XB towards new games flooding the market with used copies which in turn means that if publishers want to keep selling new copies and making money they have to lower the price to complete with them.

Yes, playing the demo I'm salivating to buy a Pikmin 3 and I wanted a physical version, sadly they are being sold for 400 BRL (~70 USD) or more. I bought my MK8 second hand to avoid full price, but knowing current our delivery/importation are facing issues thanks to covid I have no hope to buying a Pikming 3 in grey market for less than 70 USD for a good one year or so

Xenoblade RE physical are still sold for like 70-75 USD on grey market and I sadly haven't yet found a single soul reselling it. At this rate I will end buying both digital

I partially agree, in a sense that scarcity plays a key role as well, but it's still part of their overarching strategy of creating unique selling propositions. That said, I also agree it doesn't apply to every game made by them in 100% of cases, but simply because with some games they don't need to to reach their goal.

I'll comment your counter examples. With Mario Kart I disagree, each entry in the series has its distincive feature to set it apart and also they change drastically the handling with each entry to the point each games feels different: for double dash the "uinque" factor is the two-player kart setup, for Mario Kart Wii it's the motion controlled based handling, Mario Kart 7 added the paraglider and areal sections, in Mario Kart 8 it's the course design with gravity inversions. Also just look at Mario Kart Home Circuit, another example of a game based on a unique proposition.

I agree on the other hand you don't see that kind of effort to reinvent the wheel with games like 2D Mario, Smash Bros (you can also add Pokemon), but in that case the "unique" factor is granted already by the fact that there isn't really any other game to compete directly with them on the market. You may call it "brand recognition" and to some exent I could agree but it's more than that...every element of 2D Mario's gameplay is so iconic that you could consider it a part of the brand per se. In other words, imagine seeing a golden block in mid air with a question mark in a completely urelated context (say in an Assasin's Creed game) or a spinning turtle shell. You would automatically have an expectation to how interact with them although contextually it wouldn't make any sense. That's to say that those games are already so unique and recognizable they don't need to reinvent them every time.

As for the argument of games like Luigi's Mansion 3, Astral Chain, Links Awakening, Fire Emblem, .. I've never said they don't drop prices because all games sell regardless, but rather because they want to sustain the proposition of those games as "unique game experiences" even at the cost of selling less copies, because that way they can re-purpose those game even years after they were originally released. See the 3D Mario All-Star collection...three old games re-released with little to none technical improvements, still sold for full price. Since you're mentioning them Links Awakening is a remake of a 25 years old games, full price; Fire Emblem Shadow Dragon, a localization of a 30 years old game -> special edition, full price. etc. etc.

Because Nintendo wants to maintain the image that their products are higher quality or premium in a sense. It's also why 3d Mario all stars will end selling in March. It's because Nintendo thinks it's devaluing their IP so they are saying we are gonna throw you a bone with this deal but don't get used to it. It's kinda like apple where you know somethings are priced way more than they should just to maintain that image