Earlier quoted context omitted.
They can and do build them. The problem is that at intersections the normative behavior of American drivers is to queue and wait for your turn. Roundabouts assume a different behavior based on jumping the line. Thus there is a lot of unpredictability regarding other drivers due to generations of driving patterns developed in diverse regional driving cultures...many of which are distinctly not-urban. In addition, this…
Perhaps they need to start building more roundabouts on smaller intersections, and improve education in driving schools. Then give it time (decades).
It has a lot of intersections.
Reconfiguring intersections is expensive and disruptive. Stop signs and traffic lights take less space and are often the simplest thing that might work.