I totally see your point here. On the other hand, I left Philly in 2014 after getting laid off from a remote job. I could not get a job in town that utilized my skill set and paid me enough to maintain my family's costs.
From my perspective, there were only 2 games in town for people with specialized tech skills - Penn or Comcast. I'm sure that's not entirely true. But that's what it looked like to me.
The only place I could get hired (and maintain income) - Google. But Google doesn't do remote work, so here I am in the Bay Area. If Amazon comes to Philly, short term there will be costs if the city doesn't negotiate things properly. But long term, Amazon being here will mean other tech companies will come to poach labor. It's what happens in Seattle, Boston, the Bay Area in general.