YouTube video to repair screen rot

This may be rhetorical, but why did they use that PVA material in the first place, given that the solution provided in the video just places the lens over the CRT glass with nothing but air in between? (Rhetorical answer: they didn't foresee the breakdown of the PVA material into it's eventual "cataract" state after X number of years?) Could adding PVA between the lens and CRT just have been a convenient (easy) way to keep dust and particulate matter out? It did seem, in the video, there was some significant extra time involved in making sure that (before applying the sealing tape around the lens) it was absolutely dust/particle free. And using PVA as a clear sealant may have made this step easier when mass producing CRTs. I have two ADM-3A terminals: One is severly rotting, while the other is in pristine condition. Go figure. Eric