That little bit probably saved the movie, since the shark never worked. 90% of the time the shark is “there” it’s just the music. But that’s all they needed.
Eh...it wasn’t about the Shark, really, was it? It was the expectation of when it would appear from the deep!
Just like the movie “Aliens”...they didn’t show them all the much, but having them just out of sight coming for you with malignant intent was enough to make you squirm!