There are issues other than just speed, but it's not a matter of bad decisions, unless you mean bad planning decisions. The autobahn is a great example: it might be really fast, but how many pedestrians ever have to cross it? How many entrances and exists are you finding per mile? The autobahn is pretty safe, so the speeds can be high. In a similar fashion, pedestrian deaths are rare in US highways, because it's unlikely you are going to find a pedestrian in the highway.
But compare this to, say, any of the deadliest roads in the US. They all have a pedestrian use case: People need to cross them. And yet, their lanes are as wide as highway lanes, are often at least 4, if not 8 lanes across, and so straight that, once you take away pedestrians and traffic, the design feels like an autobahn. They are often rated as 40mph streets, where people might do 50 or 60. A street like that will kill people if they try to cross, as many forms of failure lead to a 4000 pound vehicle going fast colliding the pedestrian, and that's often fatal. If there is a real pedestrian use case for the street, either the pedestrians need an easy way to just never step on the asphalt, or affordances that lower the risk need to be added in.
Again, basically every lethal mile of road in America has the same design characteristics and use cases, which aren't shared by safer roads. So it's not that no road can let you do 60mph: It's that too many American roads let you do at least 40, while pedestrians have to cross them. You might as well say that deaths in a very narrow bridge with spikes at the bottom is a matter of lack of education in funambulism.