Why do Fractional laser results not last long?

I found this study on fractional devices, PMID: 20166157. Take a look at the photo of this patient Before, 3m, and 2y later. 3m later, seems like massive improvement, but 2 years later she looks almost same as before treatment - with slightly less wrinkling. Normally people don't age like that in 21 months (3months to 2 years post). Makes me wonder whether at 3m, there is significant micro-swelling which results in skin looking nicer/plump but skin actually hasn't improved that much?