Town I moved from 3 years ago had a intersection with 4 way stop signs. Huge backlog of traffic during rush hour and you could sit there for 15 minutes sometimes, a quarter mile away. Traffic would pass through from larger towns nearby out toward smaller towns. Big argument in the town about putting inn a circle or a light. Simulations were run using peak observed traffic. The lights were expected to keep you stopped for at the most 3 minutes during rush hour. The circle folks won. A year later, no rush hour clog. You almost never need to stop and wait now, even at the busiest times. It was designed correctly for the traffic.
The problem you run into with a lot of circles is that they've been there for years, and were fine with earlier levels of traffic. But increased population and traffic means congestion, and a lot of times the taxpayers don't want to pay for an expansion, and the landowners around it don't want to give up the property. At least they function just fine in power outages.

A few of the older ones I know of are smaller, not designed for long rigs, because they go back 100 years or more.
Newer roundabouts are actually designed to be smaller on purpose, to enforce traffic to slow down. Older traffic circles were larger and there were a lot more accidents on them, and traffic safety folks started replacing them with lights, which were less efficient but had fewer accidents. Eventually roundabout design ideas led toward smaller ones, which tend to decrease accidents by about 75% less than lighted intersections.
There will always be people that don't know how to use them. I see folks run red lights, turn left from the right lane, and do plenty of other stupid stuff at lighted intersections, too. Got passed by an a-hole in a pickup the other day on a 5-lane rode. Both lanes going our direction were busy, so he jumped into the center turn lane and blew by about 4 cars. Speed limit was 55, we were all cruising along about 65, and he was doing about 90. He didn't even need an intersection to properly demonstrate "stupid. "