Stadiums need upgrades, and repairs, almost constantly. The idea that you can control a pro team for 30 years is ridiculous. It's like telling a $10 billion dollar company that you'll build a new road near their headquarters if they sign a binding agreement that they won't leave the state for 30 years. Especially when the company knows that based on past history, in 10 years, the road will have to be repaired and upgraded, and the city/county/state, whatever, is saying; "Screw you! You want it? Pay for it yourself! If you don't like it, lump it, because you have 20 years left on your agreement, and it's not negotiable."
Wisconsin/Milwaukee County/City, has a history of drawing lines in the sand, and watching a seriously good tax resource bolt out the door because they failed to recognize that they don't have them by the short hairs.