plowing straight through the center of the roundabout as if it weren’t there

is there nothing in the center to prevent this from happening?

It's probably not universally preferable. Like I said if you don't walk fairly quickly then they're probably worse than an intersection. For me though, I can move between traffic without having to stop traffic like at an intersection. At a four way intersection, you have to wait for the walk sign, entirely freeze traffic, and people sometimes pull into the crosswalk rather than stopping before it like they're supposed to. Occasionally they run red lights too. Alternatively you can risk crossing without a walk sign but that carries a lot of risk. People also drive close to full speed through intersections, so it's a lot harder to time a crossing and react as a pedestrian.

At a roundabout, it's like crossing a one way street that people drive slower on. They won't stop for you, but you only have oncoming traffic from one direction. Gaps in traffic are pretty normal so you just have to wait for a decent one to cross rather than waiting for a traffic light to complete a full cycle so it can make a gap in traffic. Finally vehicles are more predictable in roundabouts than in traditional intersections because they will just keep moving forward rather than stopping and driving based on the light pattern which they may or may not choose to follow.