Why not? Even if he technically has power over the mushroom kingdom, it's not implausible to imagine that it'd be more politically expedient for him to go down the kidnapping route. There could also be secondary reasons for the kidnapping
Firstly, the Mushroom Kingdom must be ruled by some king or queen, otherwise it wouldn't be a kingdom at all. So, who is that king/queen?
Let's look at a feature common across many Mario games: Bowser's Castle. How did it get there? Obviously it was made for Bowser, given all of the...
In Super Mario Oddysey, you can obtain a power moon by scaring away a hat ghost by capturing a paragoomba, and scaring him off. How? Would a shepherd run if confronted with a lame sheep being ridden by a friend of his? Unless goombas are more powerful. And, if they are powerful, why is their...
Basically, post silly rules of anything (a country, a web forum), that are not explicitily stated, but are logic conclusions of the rules they did write down.
For example:
4chan :- no non-human apes.