Roundabouts are best with a range of traffic from very sparse to intermittent. Always packed from all directions doesn't work because throughput is structurally limited and worst case wait time is infinite. It's kind of like a cloverleaf junction, very functional until you hit capacity limits, then not very functional.

In most of the Los Angeles area, there's not room to drastically expand intersections to build usable roundabouts, compressed roundabouts are even worse at throughput.

Multilane roundabouts exist, but they're tricky to navigate and would be tough to have high throughput for if most people want to continue traveling in the same direction after the intersection.