If you actually think about it, it’s absolutely makes sense. The Autobahn has additional stopping lanes for broken down cars and several meters of grass to each side, which means you can safely drive hundreds of kilometers an hour while still being able to see obstructions early enough to brake in time.

Slower motorways have smaller setbacks, but still enough to keep their speeds.

City streets where you can’t see people entering the road in time to brake usually have relatively low speed limits to reduce the braking distance as well as the damage caused by a collision.

But if the visibility or braking distance are affected due to weather or broken streetlamps, it’s up to you to slow down accordingly. But even for situations like that traffic planners usually add additional signs, it’s common to see roads with signs that say

/❄️\
(60)

to warn people to drive slower when the road is freezing or signs that say

/🦌\
(50)
[400m]

to warn of crossing animals in the next 400m and set a lower speed limit.

The same obviously applies when it’s not crossing deer but crossing pedestrians.

Actually, in EU countries the law explicitly says you have to drive slow enough to react to unexpected changes on the road. If you as a driver hit something or someone, you are automatically at fault because you violated that law. There is an incredibly high burden of proof required to not be at fault as a driver.

But that’s usually not an issue, because road planners are only allowed to set speed limits that are low enough that drivers can actually react to unexpected changes. Which is why e.g. the Autobahn has a separate lane for broken down vehicles and significant setbacks and green areas to both sides of the road so you can see from a long distance away if something is in the road.

Slow. Down. That’s all there is to it.