The presence of huge datacenter facilities in NoVA near Dulles greatly predates Amazon AWS/S3 or any significant Amazon presence online, except for its online store. Huge amounts of construction occurred prior to 2002. The fact that there's tons of dark fiber and it's easily trenched in green field type applications there is why it has continued. It reached a certain tipping point that a dozen square km of NoVA became the defactor carrier interconnect point for anything on the US east coast (outside of the NYC/NJ area).