I don't think it is because they are stubborn but they truly believe completing the game is meant to be the reward.

In any case they should do it to satisfy trophy hunters lol.

I don't really care about achievements that much. Although I think NX will have some achievement system but it will be different from what MS/Sony have

They should expand on the stamp feature. That is more fun and usable.

Achievements sucks. Plain and simple. I wouldn't want them to copy a crap system.

Its pure stubborness they don't. Like many other things nintendo avoids. Nintendo doesn't realise you can be both different and still offer what the other companies provide.
From a business standpoint they should have it, achievement hunters buy games, lots of them. Not only that but lots of people like them so why not have them?
Oh and if your argument is "I don't like them, so Nitnendo shouldn't have them" Then you need a better argument. They're avoidable for those who don't want them and there for those who do.

They re too Stubborn.
Most people like the system though.. its something nintendo should have.

I dont see whats wrong with just listening to your users, and giveing them what they want.

Nintendo really doesn't like to be the last at using a great idea. (and when I say great, I'm talking on the business side)

They'll do it one day, like they finally used disc, or Internet, or DLCs, etc

They have said their reasoning before on numerous occasions, if I recall correctly, that they want people to play their games for fun and not out of some stressful obsession to collect digital badges that, in the grand scheme of things, mean absolutely nothing in our lives.

Hey, I enjoy getting things too, but it doesn't really matter down the road. I used to have a 360 and I don't even remember the things I had for all those games. I play steam /pc games about as often as Nintendo ones and I don't even know what things I've collected/unlocked as I don't really care. You care and that is fine, but I suspect the majority of us Nintendo fans don't care that much about universal systems or, at the very least, aren't bothered by a lack of it.

I think they're stubborn, but they really should embrace it, and possibly build off it. Wouldn't it be cool if getting so many "trophies" or "Nintendo Points", whatever they want to call them, actually MEANT something? Like you could use the points to unlock rewards, or amiibo related stuff, or get stuff added to your account for discounts? I don't know, something more than just bragging rights...