Bowser kidnaps the princess because he's an anarchist who is trying to topple the Mushroom Kingdom's monarchy.
Mario tries to rescue the princess because he read some theory online and is now a monarcho-bolshevik who wants to become the General Secretary of the Communist Party of the Mushroom Soviet Socialist Republic under Peach.
Luigi is an anprim hence why he's green. He's dating Bowser, obviously ("gay Luigi", "so long gay Bowser"). He only appears sometimes because he has a strained relationship with his brother.
Wario and Waluigi are gay married anarcho-capitalists. Self-explanatory and obvious.
