The fact that it took until 2024 for the case to resolve shows how long the wheels of justice can take to turn!
Criminal, especially a death row case, can take 20+ years to exhaust every level of appellate review. In Illinois there are at least nine levels of review available to you without going through second rounds of review, state habeas, and collateral attacks like applications for clemency, pardons etc. If you're not paying for lawyers, expect each level to take around two years or more.
To clarify, they spent decades litigating the same fundamental issue for each year’s tax filings, with each filing year taking multiple years to get to court. The plaintiffs won every single case until the government finally settled all the remaining tax years for that amount. Each year prior was worth hundreds of millions.