In fact, the healing from a pneumothorax often involved adhesions to the chest wall and renders that area of the lung LESS likely to have further problems.
What one does not want to do is to encourage a diver with an anatomical or metabolic problem which strongly predisposes to pneumothorax to dive. A significant anatomic problem (congenital bleb or "blister" on the lung) will be picked up by the scan. The major genetic problems (alpha-1 antitrypsin deficiency, connective tissue disorders) will be picked up with a family history, and a personal history of more than a single manifestation of the disease.
Many people with a significant smoking history would not have normal high-resolution CT scans of their lungs, but nobody is out there telling them they can't dive. There is rational risk assessment, and then there is liability-paranoid risk aversion.