Anycast is part of the reason. According to the Wiki “Anycast is a network addressing and routing scheme whereby data is routed to the topologically “nearest” or “best” node.” It probably doesn’t hurt that those organizations have a business interest in fast performance as well.
“The performance aspects of anycast routing have been compared to traditional unicast routing based techniques. We have shown that, depending on the traffic load and networking environment, the use of anycast routing can reduce the overall bandwidth utilizations by forwarding message traffic over shorter paths. The simulation results also indicate that anycast routing can ease the configuration and management required to achieve a given level of robustness and can reduce connection setup latency and message packet delay.”
You can also find some good information with the article Anycast – Three Reasons Why Your DNS Network Should Use It