For one, by simply reading the feature list, it says "it'll be there on the lock screen". To me that meant when I would lock my screen, when I go to unlock my screen it would be there. The double-tap home key option was not mentioned (or I didn't see it written anywhere other than the picture). Now I know how to access it and it is wick-tastic!
Probably because 5.0 doesn't come with an instruction manual, and most people would assume that the camera icon would simply be available on the lock screen without having to manually make it appear. It's supposed to be a feature to allow you to take pictures quicker and easier, yet they make you do that unnecessary extra step.