You are right that there are many ways to play Mario on many different devices, and I'm not arguing that focused gameplay in front of a big tv isn't the best way to play for extended hours, but for ten minutes waiting in a queue or on the subway (when there is an internet connection available - don't get me started on that because I'm not a big enough fanboi to be happy with that situation), it's much more convenient than carrying along a 3DS. I think Nintendo did their homework on how people will play this game. It's accessible enough to play in short bursts, which suits mobile gamers.
I do respect that you don't see any depth in this. That's fine. I know that enjoyment of games is very subjective. I'm biased in that I grew up in the golden era of 8 and 16-bit 2D games, so I'm aware that this type of game has more appeal to me than others. (Nintendo probably knows that my demographic is more likely to convert to a purchase as well, but I digress) I've tried to stay engaged with recent stuff on Playstation, but triple A titles require large time commitments and have lots of grind, and hence don't appeal to me. This does.