One can imagine if the bid process is sufficiently competitive & transparent, if HQ2 brings $10b in economic good, cities might bid eachother down asymptotically to offer $10b in incentives, which in net would result in nearly zero economic good for the winning city or the parent country, and transfer all that value to Amazon & it's shareholders.

There's also the concern that negative impacts are being ignored, such as increased demand on infrastructure, ala the Olympics, wherein by most accounts the winning city actually winds up economically worse-off.