These two locations will allow us to attract world-class talent that will help us to continue inventing for customers for years to come.The rationale for this whole exercise was that Amazon plans to grow at a rate that they think will outstrip the supply of skilled labor in Seattle, and the deciding factor in picking these locations was that they think they can hire thousands of programmers and other professionals to work in them. (Well, there was also the billions in tax incentives, but mostly likely all the cities and states on their list made similar offers.)
And this explains why around the world mega-cities continue to swell while smaller cities languish. Companies headquartered in smaller cities -- Kellogg's, Corning -- have terrible trouble recruiting executives, largely because executives are married to other professionals who can't find jobs in a small place. The way for big corporations to thrive is to locate themselves where there are lot of educated workers to choose from.