Road speeds need to be a tradeoff between safety and convenience. Unfortunately, in our mind safety and convenience are not just quantitative things, they carry moral connotations. Safety is good, convenience is at best neutral.
Until people develop a good framework to express this tradeoff, speed limits will be more or less arbitrary.
What people miss about this is that there is also a slightly awkward bend at mid-way point and it isn't unusual to see a car lodged into the fence that runs alongside.
Sometimes the speed limit is based on statistical information that may not be obvious until one day you are the fool who thinks he knows better.
It's long since been established that alerting drivers to specific hazards at or before those hazards is far more effective at reducing the hazard than dropping the speed limit or slapping up a "windy road" sign far in advance.
Ironically, there is a low bridge a mile before this bit of road with huge signs alerting truck drivers that it is quite a bit 'lower' than they might be reckoning on.
Guess what, it still gets hit - so much so there is now flashing light signage in addition and, thus far, this has also proved ineffective.
I'll save the red traffic light signal example for later...
Until we can all work from home and use replicators to create our stuff, transportation will be a huge part of the production side of society. Speed limits affect that directly.