If they didn't have to retake the test they would have 0 stress because they'd be done, so you can't really claim there's less stress. Also many students likely already crammed enough knowledge into their heads for when they took the original test, and are now forced to retain all of this for multiple weeks, i.e they have to put in a lot more effort studying for little to no improvement in score (yes students cram for tests and don't retain information, that's just how testing works)

It also means you need to go through the traumatic and stressful experience of taking the test again, when you thought you were already past it.

Double edged sword I suppose. If you felt you did poorly you now have another chance to do well. But if you felt like you did well then you'll probably get a lower score.