This may not be entirely correct, but I believe that because of the type of solvent used to keep the paint liquid in the can and as it's sprayed on, it helps the paint actually bond with the plastic as it dries. Sort of like PVC cement. So, instead of flaking off over time, it would actually be difficult to remove without removing a layer of the paint/plastic that are bonded together. I would think they'd call it "Fusion" for a reason.
