It depends on what part of the country, Midwesterners have lost diversity but I can tell someone from Minnesota or the Dakotas from someone from Kansas, for example. And the plethora of New England accents, even just within Boston, is still around.
True, and it's not to say accents are dying in the US, but I do think they're conglomerating to an extent. Case in point, ages ago one could tell the difference between somebody from Charleston and somebody from Savannah, despite such a short distance 'tweenst them, or between Manhattan and the Bronx. What we've seen is super-state collections of accents mixing and merging (some disappearing, and some sticking around) into dialectal continua. The distance one has to go to hear a distinct dialect within the same state or two has grown wider, partially I think due to greater facility of travel and overall development spreading things around. And of course, the media does have a role to play here in terms of established "standards" of "News"-speak arising to seek maximum intelligibility in various regions.