Or maybe they average about twice the mileage that we do.
I will say up front that I've never had the pleasure of visiting GB, but I suspect it has more to do with the speeds involved. 45-50 mph is common speed limit on city boulevards, (which are commonly exceeded by 10 mph) Speed limit on a section of Highway 130, not far away, is 85 mph. Just recently had most of a family killed there in a roll-over. Another local accident recently had a Nissan Altima crash *through*, not over, a concrete barrier, then flew some 100' through the air to come to rest against a shopping center electrical vault. Needed a forensic team to determine the remains were of an Altima. 4 dead.
Some time ago, a local policeman told me his department averages at least one citation per day for speed in excess of 100mph.