The article mentions that the U.S. focus was deliberate in order better assess each map's priorities: "we want to look at areas where the maps are most likely

The article mentions that the U.S. focus was deliberate in order better assess each map's priorities: "we want to look at areas where the maps are most likely to be “finished” (i.e., areas where the maps are most likely to be complete and up-to-date.) San Francisco is Google’s and Apple’s backyard, so the maps should be really good there. And New York and London are two of the world’s largest, most important cities—so they should’ve also gotten a lot of attention."