It's simple math. If you attempted to open the 10th case 100 times, there is ~50% you open the box, so you have 50 open boxes, and then you have a 2% chance of getting the 10th item each time, with 50 opened boxes that means you have only a 64% (1-.98^50) chance to get it.
To get a 95% chance of winning the 10th item (which still means 1 out of 20 people will be posting and complaining) you need to have opened 148 boxes.