Because "you" in this case is "a city government made of individuals who may personally benefit from this while not actually benefiting the area you represent".

Because "you" in this case is "a city government made of individuals who may personally benefit from this while not actually benefiting the area you represent". Also, you're allowed to bid to the point where it's a net negative for those individuals in the long run because you're just bad at math or because Amazon misrepresents the cost. While we're at it you, the single individual in charge of making this decision, may be in favor of something but your community may be entirely opposed to it, but they can't vote you out until the bid was already placed and you bankrupted the city. Also, you may be burning the current citizens for the prospect of these future citizens that the company might bring with it. You're hoping to drive out all those gross poor people and replace them with smiling rich tech managers. Never mind that you have no actual plan for where these gross poor people will go, that's their problem. You're building the beautiful city of the future, and you can't make an omelette without breaking some eggs amirite?