It's not repetition, it's the deliberate creation of a comprehensible perceptual model which lives in the sweet spot between trivial prediction and surprise.

Repetition is one way to enhance predictability. Stock musical transformations - modulation to a related key - are another.

This is a known thing in perceptual psychology, based on something called the Wundt Curve.

Too little novelty is boring. Too much novelty is incomprehensible and frustrating. Just the right amount is an enjoyable sweet spot.

Of course this varies for different listeners. If you're a fan of modern "squeaky door" contemporary classical music you're going to demand a very complex and unpredictable experience that pop fans find unbearably unmusical - and vice versa.