This. Just like people used to buy a Playstation for Madden, so too do people buy Nintendo consoles for Mario or Kirby or whatever.
This too, but it's why they don't need BF6, RE9, etc. Since Wii-era, Nintendo's vibe with third party stuff is that it's a bone they're throwing out there to lure in undecided casuals. I don't have any numbers in front of me, but given the sales of something like a Mario Kart 8 for Switch, they probably made more off DLC packs for that, than they did any third party title on the platform. Maybe even multiple combined..