Re: It's the jobs
Yes, it will cost the city and county, but if they do not pass a significant amount to their citizens via taxes, it might be worth doing.
It's a gamble and those entities have several things being dangled in their faces.... for example "up to 50,000 jobs" so unemployment might/will drop and there is employee taxes, spending, etc. to happen. We won't get into if Amazon actually will pay a living wage those "up to 50,000". So, there's also "votes" for those city and state "fathers" who are bringing this prosperity to the populous.
But they won't talk about things like more traffic congestion, etc., only the benefits. Yes, it can be a good thing for a city/county/state. It can also be a hidden time bomb that will come back to bit them later.
Everyone wants a miracle, two chickens in every pot, etc.... Not everyone (most?) will only get maybe half a chicken....