https://gizmodo.com/amazon-is-now-ditching-on-seattle-plans-too-1832947313/amp
Their multiple headquarters and other expansion plans were just a scam on a corporate level. Amazon talked about making big investments, and hundreds of cities fell over each other to give Amazon shitloads of data on their development plans, economic and otherwise. Amazon can now go back to these cities with far smaller plans to put in a satellite office or some such, and have huge leverage in negotiating the deal because the company knows exactly the cities' plans for the area. All this at no cost to Amazon, but of course they can sell all this data to other companies.
http://inthesetimes.com/article/21571/the-hq2-scam-how-amazon-used-a-bidding-war-to-scrape-cities-data
Amazon is rumored to be signing a pretty big lease in Bellevue (aka Seattle's second urban district), so it's more about saturation than a pullout.
Turns out you can't have 40K workers in Downtown Seattle and expect similar growth in the same area.