You actually care about the plots in a Mario game? Why?
These games are pure gameplay. Super Mario plots are a total afterthought to Miyamoto. That's why Mario has no backstory, hardly anyone ever speaks more than a random exclaimation, and the objective is always the same.
I like how the story is exactly the same each time. I'm almost disappointed when they get all self-referential in games like Paper Mario 2, with Bowser talking about his 'annual princess kidnap'. I want them to tell the same story every time as if it's the first time they've ever told it.