Here you can read about similar enzyme-biodegradable plastic developed by US scientists. Instead of using an enzyme spray, the enzymes were integrated into the plastic itself and protected from damage by "wrapping" them in a layer of specialized coating. The enzymes get activated when certain environmental conditions are present, more particularly a certain level of heat and humidity. Until then they are not degrading the plastic.
I understand your approach is different, it seems more instant and user-friendly, I'm not sure why the mentioned scientists chose to implement enzymes into the plastic itself instead of applying them externally to the plastic by spraying or other means. But my guess would be that when you implement the enzymes at the molecular level, the extent to which they degrade the plastic is way higher compared to external application, also, perhaps that's why the enzymes were additionally protected from the environmental influence, this is done in order not to degrade the enzymes themselves as they are sensitive to the temperature and other environmental factors. If you sprayed the enzymes they would be exposed to the environment and might get broken down before they can do any damage to the plastic.
The article also talks about future possibilities of making plastic with programmed biodegradability. Maybe the enzymes could have an implemented molecular timer or somehow be activated remotely by a switch of a button.