It was vacated on a technicality, not a matter of fact.
You are implying that the decision to free Lula was politically motivated. How can you then be sure that the decision to charge Lula was not politically motivated?
So what? No matter what "side" happens to be in charge at any given time, sane people would never want to live in a country where serious concerns of due process could be dismissed as a "mere technicality". That's just a recipe for show trials.
So what? I didn't say he should go to jail or that the verdict should have been vacated... but I wouldn't have a lot of faith in the political process if a major political figure most likely only survived a criminal trial because of a due process issue.