Repetition as Rehearsal
Songs often repeat verses, choruses, and hooks. This repetition acts as a form of rehearsal, strengthening the memory trace. The predictable structure also provides cues that help retrieve the next part.
The Catchy Chorus
In pop songs, the chorus is repeated multiple times. Hearing it again and again, even passively, reinforces the memory. You might find yourself singing the chorus even if you don't remember the verses.