I mean, the point of any bundle is that you guarantee money from the single purchase instead of relying on two separate purchases, potentially on separate occasions. Would *everyone* have bought Mario Kart for $80? No, but they'd get it in the bundle that's only $50 more.
It is literally the launch of the console. I just don't buy the argument that the reason MarioKart sold is because the bundle exists. Much less why the bundle is significantly cheaper than buying separately.
Mario Kart definitely sold a lot because it's Mario Kart and it's a great game, but I'd bet more than a few people were persuaded into getting it because it was cheaper in the bundle.
It is basically an unprovable statement. But I will point out effectively selling MarioKart World at $50 is leaving money on the table given how much Mario Kart 8 sold and it was basically at $60 most of the time.