Roundabouts (circles, rotaries) are great for light traffic (and if everyone knows that all roundabouts have the same rules, i.e., everyone entering must yield), but they lose efficiency in heavy traffic. Then they start backing up, not enough breaks in the circle for cars to get in, governments put extra layers of organization (more inner lanes, declaring certain roads have the right of ways, traffic lights to break up the jams) which make them too complicated.
Jersey used to have lots of 'circles', but most are gone now replaced by giant intersections governed by traffic lights. Also, we tend to ban left turns. Gotta go right to make a left.