But that would be expensive, compared to just painting the road. And so we get into opportunity cost. Resources are finite, and even deciding what to do costs resources which you then can't expend on doing something.

In my country you can't just paint the road, at all, the minimum intervention is a lit crossing, orange lamps at each side, called "Belisha Beacons", which together with the paint forms a mandatory (ie if somebody is on the crossing or appears to be intending to cross vehicles must stop) crossing. This means you need electric power (for the lighting) and the resulting crossing is significantly safer but more expensive.

Even deciding whether, and how, to allow the simpler painted crossings is a significant opportunity cost, it would require legislation, and the government has other things it wants to do (e.g. sell off irreplaceable cultural treasures to spite enemies) with that legislative time.