Most MBA applications never ask this question outright : Why do you NEED an MBA, not just WANT one.
So most applicants skip the proving altogether. They assume the reason is obvious. It rarely is, not to the person reading your file at 11pm, application number 47 of the day.
There’s a real difference between wanting an MBA and needing one. Admissions committees are not in the business of handing out seats to people who’ll do just fine without them.
If your application reads as someone who’s already got it all figured out, you’ve quietly told the reader something you didn’t mean to. That a seat would be wasted on you. That they’d be teaching someone who has nothing left to learn.