That seems like an obvious question that went unanswered in this NYT piece. It did talk about how this would increase Amazon's bargaining power if it could play off two cities (and Seattle) against each other, but it did not raise the question of the initial commitments. In many of these bidding wars, the winner ends up losing by giving away more in concessions than it could ever hope to get back from the investment generated. It will be surprising if this is not the case here.