The creators likely chose this nonsensical phrase for several reasons:
* Humor: The nonsensical nature of the phrase adds to the comedic elements of the movie.
* Childish Appeal: It's a fun phrase for kids to say and remember, even if they don't understand its meaning.
* Magic and Mystery: The unknown origin and lack of meaning create a sense of mystery and intrigue surrounding the magic.
In essence, the phrase is a magical "password" or "key" that unlocks the power of the bedknobs and broomsticks magic, without any real world linguistic or magical significance.