Combination of things. Could be crap materials but that can happen to the best cast material as well. One thing many are not aware of that causes a LOT of damage to vinyl is dew (and the acids and other chemicals in it). Of course UV exposure also causes damage as well. My guess is the reason you see wraps and printed vinyl do that on the white unprinted areas more than printed areas is the solvents from the ink causes some changes to the materials. it seems counter-intuitive to me though, I want to think the white would reflect the light more and the darker colors absorb it more but maybe that is just the "heat" of the light and the actual UV parts work just the opposite? I've had to remove wraps on hoods where unprinted white areas were a nightmare breaking into a million pieces and the paint underneath is ruined there but the darker printed areas come off much easier in large sections and the paint there was fine.