Because its on a busy intersection and people are idiots. I've used it hundreds if not thousands of times on my bike, not to mention as a pedestrian. I would not do either one if not for the stop signs. I've seen so many idiotic interactions over the years that were only mitigated by the slow speeds starting from a full stop.

People like to zoom down Cesar Chavez especially at night when traffic is light. It would be a death zone for pedestrians and cyclists under normal traffic circle conditions imo.

Also, there are heavily used crossings for two different elementary schools within a few hundred feet of this traffic circle. The impediment to flow of traffic is probably intentional for that reason alone.