The speed limit increased but the driver's speeds did not. The reason goes back to the principle of the 85th percentile rule. Vehicle condition - good tires, engine in good shape, etc. The same drive who will do 75 mph down the interstate highway on a clear and dry day, is likely the same driver who will do 55 mph on a rainy night. The final verdict is that speed doesn't kill.
Speed generates revenue.
A real example of this is the unmarked police car. We all know that everyone slows down when they see a police car. The unmarked police car is proof positive the governmental agencies are aware that the speed limits are too low and people are going to exceed them. The way to capitalize on these people is the unmarked car whose sole purpose is to essentially entrap drivers who are part of the 85th percentile rule. The governmental agencies aren't the only group responsible.