May harken back to the adoption of net promoter scores. Back then so many companies were giving such terrible service that "average" was bad. So then every interaction needed a 10 out of 10 so you could secure those promoters. So many people came up working at companies where anything below a 9 or 10 reflected bad on their work it doesn't surprise me that max scores became the new norm. You don't want to get any fired, do you?