- Most music is highly repetitive, often recycling 2 or 3 short segments (chorus, verse) with minor variations to fill out a whole song. Coltrane is known for his avant-garde composition, and even he repeats (often on a much smaller scale than a pop tune).
- The work of being a musician is repetitive. Learning (memorizing) songs takes reps! Then you've got to keep them fresh, teach them to new band members, etc. You probably have a limited book, and you know what the crowd pleasers are. Unless you're big enough to have a following cutting a song you're sick of isn't a problem, but filling out a set might be. Between rehearsal, gigs and practicing at home I probably play through most of my band's book at least twice a week.
- Being a musician is very physical, which means you're drilling exercises in your daily routine. As a brass player, I run more or less the same set of warmups, range builders and flexibility exercises every day. Drummers do rudiments. String players have their own shtick.
As far as listening to music, I don't typically put something on repeat unless I'm trying to transcribe it. But I'll listen to a song, and there's a chance it'll play on repeat in my head all day (or all week!). Steely Dan and LCD Soundsystem are particular earworms for me. It wasn't until college I realized this isn't true for many people.