If you look across Europe where most nations have had as much time as the other to learn the rules (which is now about 100 years), there are still big differences.
Cue the difference between German, Austrian, and Hungarian drivers.
Germans: can be very aggressive at times. Austrians, only if you're in the wrong lane. Hungarians: fear for your life if you ever try to overtake someone ..
Some of this is propagation of cultural myths/stereotypes. In a country of millions of people there will be millions of people that don't conform to these blanket statements.
In the US, states and cities have their own driving stereotypes that don't fit neatly into an easily summarized national driving style.
