[ProCynic]

First someone who is affected by the law has to challenge it, then the challenge has to make its way through the appeals process until it reaches the level below the supreme court, and then finally the supreme court must decide to take up the case. It's a fairly involved process that only ever gets applied to a small fraction of laws. But the filtering process tends to select laws of questionable constitutionality, so it's fairly inevitable for something like the ACA to end up there. Though it helps to have a powerful interested party pushing a case through the process.