Earlier quoted context omitted.
Traffic rules basically give drivers a way to deal with other vehicles going different speeds. So a the driver of a scooter going 20 mph and the driver of a car going 40 mph can share the same road, just like a driver of a truck going 40 mph can share the road with the driver of a car going 60 mph.
And yet, that same car can go 80 or 90 or even over 100 mph, which would be illegal on any road. Why?
On a steep enough descent, a cyclist could get up to speeds beyond 50 mph, which really isn't safe given the equipment.