On modern Apple devices, the HW indicator light is wired directly between the power rail of the camera module and ground. Turning the camera on via software energizes the power rail. The only way that the camera is on and the led is not is if the led has burned out.

This is a "nothing-up-my-sleeves" implementation, it's not really possible to hide anything weird in the complexity. Apple clearly didn't just want a light that's always on when the camera is on, they wanted an implementation where they can point to it and clearly prove that the light is always on if the camera is on.