I just wondered about this once. Why is it that in the Mario games, Bowser's minions are a really diverse lot with Goombas, Koopas, Boos, Lakitus, Buzzy Beetles, Spinies, Cheep-Cheeps, Shy Guys, Bloopers, Piranha Plants, Chain Chomps, Amps, Bullet Bills, Bob-Ombs, Thwomps, Whomps, Wigglers, Monty Moles, Fuzzies and Pokeys, while the Mushroom Kingdom is inhabited with the highly homogeneous Toads? In fact, a lot of areas in the Marioverse seem to be inhabited by a single dominant species, while the Koopa Troop's reign is like that. Did the Koopas just invite all the people unwanted anywhere else to serve their king?
That does make one wonder about Bowser's motives. Considering that the main area of the Koopas appears to be a volcanic, barren wasteland, is Bowser perhaps with his aggression towards neighboring countries trying to gain Lebensraum for his people? It would explain why they seem to genuinely like him.
In fact, if you think about it, Bowser himself seems to prefer the volcanic soil, as he rarely leaves it and his castles are always full of lava. (Also, why have I never seen any geysers around there? Going by Iceland or Japan, I thought volcanic areas would often have those.) Then why does he conquer the cooler lands? Maybe it's specifically for his minions' sake. Why are so many of them named "King" something, if they are his minions, by the way? King Goomba, Whomp King, King Boo, King Kaliente. Maybe they are descendants of rulers who entered the Koopa Kingdom, and Bowser's predecessor insisted they keep their royal titles even when those had become meaningless. This would make Bowser himself actually a king to whom other kings swear loyalty, and therefore an emperor.
And even if this all were proven wrong, Bowser's reign still can't be the worst place in the Marioverse. There's no evidence whatsoever of corruption there, unlike, say, Isle Delfino...
And now we know why Mario invites his so-called nemesis to go-karting and sports.