Well, one can certainly blame the Daley administration, which shoved this deal through during its last term, and then coincidentally Daley became employed at the legal firm that wrote the deal.
Chicago unfortunately lacks a recall mechanism, and voters were unable to punish Daley for this plan that had not been part of his campaign, because he declined to run after his approval rating sank to record lows.
Instead of tidily blaming a specific politician and then moving on as if nothing can be done, this type of principle agent problem should be eliminated. Simply put, mayors and city councils should not have an unrestricted authority to legally bind cities.
I'd say that any contract longer than around 3 years (and/or larger than a certain dollar amount) should require direct approval by voters, or it shouldn't be considered as having been duly executed. Furthermore any terms of a contract that restrict/require a municipality to enact certain laws/ordinances (including through financial incentives) should be straight up illegal and thus unenforceable.
The problem is systemic. How would you enact such a change? Neither Chicago nor Illinois have mechanisms for citizen initiatives amending laws or the relevant charters and constitutions, so you'd need a three-fifths supermajority of politicians to agree to hobble themselves.
There are many comments in this thread assuming it's a legitimate agreement made by the "city". My main point is that in the abstract, we should not take this as an open and shut moral certainty. Rather we should view the "contract" in the same light as a real estate deed signed by someone under undue influence or otherwise incompetent.
As for practical reform, especially with this failure in court? It might still be possible to get a majority of state politicians to constrain the city politicians. More centralized government is unfortunately one of the few remaining checks in this day and age.
Unfortunately, the legal system does not work in the abstract, and particularly for anti-capitalist policies the courts don’t look kindly to making up legal theories out of thin air.
A prerequisite to any sort of reform is being able to criticize what is wrong in general principles. As I said, there are many comments in this thread just plainly assuming that it's legitimate to consider the city as being bound by this deal due to unilateral actions of the mayor. Pointing out that this is an opinionated assumption and that we could instead use other standards to mitigate the principle agent problem is my attempt at articulating what is wrong with the situation. I'd say it has much better explanatory power for what people intuitively feel is wrong here.
Chicago unfortunately lacks a recall mechanism, and voters were unable to punish Daley for this plan that had not been part of his campaign, because he declined to run after his approval rating sank to record lows.