One of the requirements for the Amazon HQ2 headquarters is a large skilled workforce.
According to Fortune Magazine to have the 50K skilled tech workers it would require the metro area to have 4 million people. Filling these tech jobs are not easy and the locations that should have the tech skilled population include Atlanta, Boston, Chicago, Dallas, New York, and Washington DC.
The link, included here, http://fortune.com/2017/10/18/amazon-hq2-top-cities/
says that it would be difficult for cities like Pittsburgh, Tampa Bay, Jacksonville, Orlando, Charlotte, Cincinnati or Denver to scale up to the 50,000 skilled workers over the next decade.
I think that makes a lot of sense and it might also exclude more blue color cities like Philadelphia.
My opinion is that if you also look at transportation and lower cost of living you can almost exclude New York, Boston and Washington DC.
Leaving the top selections of Atlanta, Chicago, and Austin.