Where do you see this? I see Greater Boston, Albany, Ithaca, State College (Penn State), Greater DC, Charlottesville (UVA), Raleigh-Durham, Ann Arbor (UMich), Urbana-Champaign, Madison (UWisc) in the 'brain gain' category, all anchored by one or more strong universities, while a few smaller metros in Rust Belt states that are missing these amenities and are on the rural periphery are showing in 'brain drain'.
VA drain: Lynchburg; gain: nearby Charlottesville, Roanoke, Richmond
MD drain: Cumberland; gain: nearby Morgantown (WV), greater DC
PA drain: York; gain: nearby metro Baltimore (MD), greater Philadelphia, State College
OH drain: Toledo, Lima, Mansfield; everywhere else neutral
GA drain: Valdosta, Macon; everywhere else neutral
The culture in the area is great, and there's no better place for a craft beer enthusiast to live. Couple the excellent job market with the low cost of living, and it's a hell of a nice place to live. Of all the places I've lived, it's by far my favorite.
I think that just looking at blobs of color is not particularly useful as some metro areas are much much larger than others.
Until you factor in cost of living. Last I checked Austin has lead in cost-of-living-adjusted salaries for the last few years.