When we were bought by an international company they also introduced customer satisfaction questionnaires with scores from 1-10 on various aspects of customer service. And it was the same: anything under 8 points was considered a negative response and weighed as such.
I think it's just unrealistic: some people may give out something in the middle (5-6) for "normal" service and more only if something was completely outstanding.
On surveys I usually give out 8 or 9 when I'm satisfied, but for a 10 there must have been something unusual (usually an incident) where they could prove that their service is outstanding.
One time with a Marriott stay I was given a note when checking out asking me to give 8 points or more if I was satisfied. I understood immediately that they were using the same system.
HTB.