I had my old Ultegra 10s chain on for almost 4000 miles. It was pretty wore, but still showed within wear limits. I changed it because I changed cassettes. Maybe folks aren't considering chainline when shifting, maybe crossing too much or something. It's on a Cannondale CAAD8 R1000 with a R700 compact. I changed the cassette from 12-25 to 11-23.