> You say that like this is a bad thing.
Probably because I believe it is a bad thing.
> Nintendo isn't just making the same games over and over again.
Let's say I haven't owned a Nintendo console in a long time (which is true-- the last one I bought was a GameCube, which was a piece of crap so I sold it to my step-sister), how would I be able to tell that 2017's Mario is any different than 2014's Mario is any different than 2011's Mario?
If Nintendo genuinely has new game play ideas, maybe they should actually put those ideas in new games. They're not incapable of this-- for example, Splatoon looks genuinely innovative-- but they're more interested in keeping the nostalgia factor than marketing new game concepts. There's one Splatoon for every 10 Mario X or Zelda X or Metroid X.
> And ultimately, the first-party games Nintendo puts out, your Marios and Zeldas and whatnot, are always very polished, excellently-designed, and downright fun games.
Possibly; that doesn't make me interested in buying them. The 1998 Psycho color remake was very polished, excellently designed, etc. But it was just an identical remake of a movie that'd already been made, and if you've seen the original there's no point to seeing the remake.
> Typically the best games on the whole platform.
Because Nintendo's great at games, or because they can't convince anybody else to develop games for their wonky-ass platforms? The truth is probably somewhere in the middle.
Just to drop a note here from the Xbox universe, the Xbox perennial first-party title is Halo. Halo 4 and Halo 5 kind of suck. Kind of suck a lot, really. But the strength of Xbox is that if Halo sucks, you can play Titanfall or Evolve or Call of Duty: Infinite Warfare or Battlefield 4 or... you get the point. And that's just in that one genre.
Unlike Nintendo, Microsoft (and Sony) isn't crippled by bad first-party games. If they were they'd probably put a heck of a lot more effort into ensuring their first-party games didn't kind of suck. So it's kind of an apples-to-orange comparison. Nintendo first-party titles are good because Nintendo has far more incentive to make them good.
> It's not unreasonable to say that Mario and Zelda by themselves sell a large portion of Nintendo's consoles.
Of course not; that's exactly what I've been saying. The company relies almost exclusively on nostalgia to sell its products. Mario and Zelda are nostalgic titles.