Loudoun was super wealthy before the data centers started springing up. It was where old VA money had their horse farms and wineries. What changed was a huge influx of very well paid tech and natsec jobs after 9/11. And as you say, data centers breed data centers. But they do not require a lot of people. A few dozen people for thousands of servers. KC is not mopping up the 5000 employees from, say, the former Sprint's headquarters with one or two data centers.