Just speculating, but maybe it's because Google, Facebook, and Amazon have a tech presence in Austin and not in the other 3 metros you mentioned?
Re:Pittsburgh Gets a Tech Makeover
by thesmallestcat on Sunday July 23, 2017 @06:14PM
(#14834706)
Google has sales and engineering in Chicago, engineering in Chapel Hill, and sales in Dallas. I think there may be some engineering in Dallas too. There are enough good people out there unwilling to relocate that you can find a Google presence in most tech corridors.
Google doesn't have an office in Dallas anymore
Austin is overhyped. There are cities in East Bay that nobody knows of (e.g., Emeryville) that have raised more money than Austin.
What makes Austin a more important tech hub than, say: Dallas-Fort Worth, Raleigh-Durham, or Chicago?
[1]: https://www.theatlantic.com/technology/archive/2016/01/globa...