If you have the LED hooked up in parallel with the chip, then you can't really do any fancy indication things like blink the LED, change colour (voltage level) etc. It's possible that the engineers wanted to maintain that flexibility.
Second, if the LED fails to a short your camera won't get any power. That means an expensive component appears to be broken when it's only a very cheap component, and you have no way to knowing that w/o opening up and inspecting or replacing parts. In contrast, if an isolated LED fails, one can still verify that the camera works via software, and choose not to send it in for repair.
Also, LEDs have a very small leakage current even in their off state. If somebody is hyperoptimizing power consumption they might choose to put the LED on a high impedence controller output rather than feeding off a power rail or similar.
Finally, the desired led might work off a configurable controller output, but that might not be the same as the output driving the chip enable pin. So you could require extra circuitry to convert to a compatible voltage/current level.
That's my guess.