No insight on Atlanta or Seattle, but Austin has had tech longer than people like to think (IBM/Freescale, UT Austin+TI Partnerships, etc), and also got on the 'hype train' early by rebranding SXSW from pure music/entertainment into 'SXSW Interactive' quite a while back (early 2000s if I'm not mistaken), so you have lots of west coast tech/media/vc 'influencers' heading there on a yearly basis getting schmoozed heavy