If anyone wants to know why this is the case: The federal government gives states money for roads. However, the federal government only gives a percent of the road budget based on the max speed in the state. The lower the max speed the more the gov gives the state. This is why speed limits are far lower than the average speed of traffic in some parts of the country.
It’s a balancing act. An artificially low speed limit costs lives, but an artificially low speed limit gives the state quite a bit of income that they need. This is why highway patrol are told not to give a speeding ticket if someone drives below X hidden speed, which differs from the official speed limit. If the officer gives a speeding ticket at too low of a speed they can face consequences. Judges have been known to give highway patrol an earful about it in court.
Eg, in most parts of CA where the max speed limit is 65, they’ll only give you a ticket if you go above 80.