People are buying the Switch to play Mario Kart. The sales of Zelda went up this week. Look out for hardware sales in the Japanese sales topic this coming Wednesday and you'll see the increase in hardware sales.
What would it have taken for you to not buy Mario Kart anyway? You sound like quite a unique case. I don't know if it's possible to outsell MK7 so early in a systems life cycle because there being nothing else to play. Do you honestly believe this is the case?
I seriously doubt I'm a unique case. While not everyone who bought a Switch day 1 are big Nintendo fans I'm sure a fairly significant chunk are people who owned Wii U and played Mario Kart 8 already.
I'm not saying it's a bad thing Mario Kart 8 is selling well. I think its my favorite Mario Kart with all the DLC and the proper battle mode.
I think if Mario Kart 8 deluxe had launched this fall a smaller percentage of Switch owners would be picking it up due to having a lot more software choices like Arms, Splatoon and Mario Odyssey (though it would still do very well). Right now there are a lot of Switch owners finished with Zelda and looking for the next big thing on the Switch.
I own ten games on the Switch thanks to eShop and I don't even have time for all of them.
Lack of AAA software? At the moment there's more quality AAA titles compared to quantity. Wii U had a lot of AAA games at launch and they sold terribly.
Lack of software in general? No, there's a variety of game genres available on the eShop that anyone can find something to play.
You're deluding yourself if you think there's a lot of software on the Switch. Third parties haven't jumped on board and there's some indie games but much of it is old multiplatform software that you could of bought years ago on another storefront.
To be fair though pretty much all consoles start with a weak software lineup so it's not a huge deal. I imagine big third parties will start supporting the Switch a little bit more if sales continue to be strong but I cant blame any of them for having cold feet since it probably costs more to port a game to Switch than Xbox, PS4 and PC due to the power difference and profit margins on physical will be a little bit less due to game cards.