A commonplace in United States (hereafter US) linguistics is that every region supports its own standard; none is the locus (or source) of the standard. Historically that is a fair assessment, for no long-term centre of culture, economy and government has dominated in the US.
Hartley, Laura and Preston, Dennis R., "The Names of Us English: Valley Girl, Cowboy, Yankee, Normal, Nasal, and Ignorant" (1999). Faculty Publications - Department of World Languages, Sociology & Cultural Studies. 25.