To continue on the matter of the whole land being a Super Mario attraction where you interact with things, not doing a ride through Super Mario attraction avoids one of the largest issue with Radiator Springs Racers: you walk through a beautiful recreation of Radiator Springs Racers on the way to the ride entrance. You queue in Stanley Springs, no issues so far.
You board the ride car, do the best part of the attraction to me, which is the drive up the mountains with great music and the reveal of the waterfalls. Then, the story goes off the rails when you enter the show building where no matter if its daytime or nighttime outside, you transition to pitch black. How does the indoor portion end? A drive through a miniature version of Radiator Springs, which you had just walked through in an even grander setting and scale. You then go outside to race at slow speeds around a track obviously designed to go faster.
By having a Mario Kart attraction set inside its own piece of Mario Universe, it avoids having a ride through the Mushroom Kingdom that guests walk around outside. On Pirates of the Caribbean, you don't walk through the Spanish Port on the way to the boat. On Haunted Mansion, you don't walk through the graveyard on the way to the Omnimover, etc. I applaud Universal Creative and Nintendo for not going the easy route and figuring out a way to tie it all together.