Because for every one dollar in incentive they give amazon they will get 1-3 dollars back.  Would you give me one dollar if it meant I had to give you three dollars?

Here's some tax math for you.  Amazon says it plans to hire 50K workers with an average salary of 100K.  That works out to 5 billion dollars in payroll.  50,000 X $100,000 = 5,000,000,000.  Multiply that by the state income tax rate of 4.63% and the State of Colorado would receive 231,500,000 dollars every year in state income tax from the people working for Amazon.  Payroll taxes that Amazon will pay would also be 231,500,000 per year.  The State of Colorado is offering incentives of up to 100,000,000 over the a number of years.  I say give them 100,000,000 so the state can collect 463,000,000 every year once Amazon has hired everyone.  I know taxes aren't ever that simple but the math favors the State of Colorado if Amazon does move here.

And this doesn't even account for the extra property taxes and sales taxes.