Well. If you put a large glass window on the reinforced steel safe to make sure you can observe inside the safe. You can’t exactly expect criminals to not just smash window instantly to take everything instead of struggling to open the safe harder way.
Making master key is also not the approach that works because unlike physical keys, digital keys can be copied millions of times exactly without any flaw over miliseconds without requiring any specialized tool on site.
Disadvantage of said system for Google would be the fact that if you do that, people can skip ads much faster and they won’t be able to do any tracking of interaction at all. For advertiser’s point of view, that would be just worse version of TV commercial.