Speed limits did increase with the evolution of cars: https://blog.americansafetycouncil.com/the-history-of-speed-limits-in-america/

It's just that your car's brakes are not the only factor at play here. So is your reaction time, unexpected conditions, and more. At elevated speeds, you may be unable to properly monitor the conditions on the road and react in unexpected situations in due time. Driving a straight road can make a driver overconfident, by it takes one wild deer or one accident in front of you to quickly come back to reality that you don't have it all controlled.