Farsala said:

It seems to me that the Mario Kart team is slacking

Well, Mario Kart Tour did just come out.  I'm not aware of it being handed to a different team and, while hardly a full game, they put at least some effort into it.

I'd been running under the assumption that the team would finish up the main work on MK Tour and then start production for Mario Kart 9 as a Switch 2 launch title.