I have to admit that I haven't encountered Robo Mario yet but I absolutely suck at this game. I'm not really bad at Mario kart games except the arcade versions. Really wanna see Robo Mario again in Mario kart arcade vr too.
There's other explanations for the characters. Like them having better things to do ; managing countries, having other adventures. Also being absent kingdoms don't mean anything, bowser might have not needed anything there so Mario didn't went there.
Oh neat that's neat. I also think that Metal Mario is an updated version of Robo Mario from the arcade gp games that's why Robo Mario doesn't appear in gp dx that's because metal Mario replaced him. And pink gold peach is also a robot made by E.Gadd.
I find the Mario and Luigi being trapped in a death theater idea more fun but eh.
When did bowser do the tourist trap thing?
Also Cranky is current dk's grandfather as stated in one of the games and Jr died. He's now bink the skeleton Kong in superstar saga. (I know for the redesign).
The bean bean kingdom shares physical borders with the mushroom kingdom so its on the same island. I assume sarasaland is too but I gave no proofs for that.
I only have two major headcanon and it's on SMB3. Remember when Myiamoto said the game was a stage? It crushed me. Then I found a solution. Bowser trapped Mario in a stage environnement with deadly traps everywhere and he watches what's happening from above. It's just set in a giant Koopa...