Because "recipe for a smoothie" analogy is too broad and doesn't help you understand how the Fourier Transform is different from a Ruby script or a bill of materials for a chair.

Not to mention that the idea of "given a smoothie, it finds the recipe" is impossible and makes no sense in the first place.

Tasting a drink and guessing its ingredients makes no sense?

Except that absolutely not how the Fourier Transform works and gives a very false impression.