More wild speculation:

1. Patterns make brain release happiness hormones, because it rewards itself for correctly guessing how the pattern continues. The rewards stop when the pattern is overly repetitive, because the brain recognizes that this isn’t a challenge to guess correctly. And then it also quickly becomes not worth paying attention to, because if it’s not going to change, it’s irrelevant to our continued survival and all.
2. This applies to anything where humans perceive beauty. A painting with a consistent color scheme or technique is nice, but just a blue canvas is pretty boring. A poem that rhymes is nice, but if it rhymes twice or thrice by using precisely the same device, then it doesn’t entice.