I don't know why Americans can't handle roundabouts. Maybe because merging requires too much intellectual exercise. Or maybe because they don't want to be forced to look up from their phones.
But roundabouts are MUCH safer than conventional traffic signals because you don't get head-on collisions, you don't get high-speed rear-end crashes, you don't have to do left turns across incoming traffic. When people screw up, it's fender benders, no injuries. A whole lot better than getting t-boned at 50 mph by some teenager playing Candy Crush.
Also roundabouts save a lot of time because you slow down to enter the circle but you don't usually have to stop. Let alone wait 2 minutes for a typical American 4 cycle traffic light.
If you drive in France, you see how much easier it is to travel with modern road design (the Europeans are 20 years ahead of us in this area). Driving is such a pleasure in the countryside because you can go hours driving through villages and towns without having to stop at a red light.