Cost. That separate road means buying land from someone and turning it into road. Do they have one way roads for rural schools in Germany? Because I looked at a few Grundschule in Bavaria on Google maps and didn’t see any.
You’ll have a hard time finding a village with literally one single road. Certainly not one 1-2k which is the size that gets the school for the surrounding ones.
It is cheaper and more convenient to have a speed camera that is active only during school hours.
And also completely ineffective at preventing anything.Heck at least use road bumps. Narrow the road only in spots so that two monster trucks if you please fit on comfortably side by side for 50-100m or such, but then it narrows down to half that for just 5m. While you’re at it build a crossing there, narrowing the roads at pedestrian crossing is standard practice in many places and it makes a hell a lot of sense. Yes, that slows down traffic because you might have to negotiate with oncoming traffic who goes first. Yes, that’s precisely the point.