I doubt that land in the downtown core is a central consideration based on the fact that Northern Virginia and Montgomery County, MD are listed in addition to Washington, DC.

Northern Virginia has a lot of land, an existing tech sector, a ton of data centers, one of the biggest Internet peering points in the world, and a big international airport (Dulles). It's not a cool place to live and work, though, the way the city is. It's family suburbs and strip malls, mostly.