I live in a state that has 55 mph limit, and I've spent lots of time in states that have a 70mph limit. everyone drives the same speed regardless, around 75-80

I live in a state that has 55 mph limit, and I've spent lots of time in states that have a 70mph limit. everyone drives the same speed regardless, around 75-80 on a straight and wide highway in the left lane, around 65 in the right lane. the sign means nothing.