I agree. We won't see Mario Kart 9 any time soon. Probably not until their next platform as a launch game.
Which is why I feel that the argument people use that says "ports don't affect the release of new games" to people who complain about them isn't entirely true. I'm generally not against ports at all, and even welcome the possibility of a select few more Wii U ports, but Nintendo more or less has treated the Wii U ports to the Switch as brand new games in their respective franchises. Don't expect a brand new Mario Kart on the Switch, nor a 2D Mario that's not Mario Maker 2. Heck, I'd say even the chances of a new DK game is slim.
I guess it's just the reality when we're coming off of a failed system that nobody bought. These technically are "new games" for the vast majority of people. Sucks for Wii U owners though.