Sony's games are on PC now. Final Fantasy restricted itself to PS5 and underperformed. Games that those platforms use to sell their platforms also come out on PC because they just cost too much to make, and there are too few of them because of how long they take to make now. Nintendo generally spends less, but they're still running into the same problem with development time, and that means their exclusive offerings will dwindle as they have to ramp up fidelity on more powerful hardware, just like what happened with Sony and Microsoft, which means fewer and fewer games that can only be played on that specific set of hardware. Third party exclusives mostly disappeared because, for the same reasons, restricting yourself to one platform is generally a stupid idea these days.
As an aside, racing games in general are rare these days, not just kart racers. My options are Mario Kart, sim racers, one step down from a sim racer like Forza Horizon, and little else. I like racing games, but not any of those. The market will come back around; I've got Trail Out right now and Aero GPX in the near future that will hopefully tide me over until someone makes racing games for me again.