Right, so this is all defense in depth. That LED is sort of the last line of defense if all others have failed, like: The exploit mitigations to prevent you fr

Right, so this is all defense in depth. That LED is sort of the last line of defense if all others have failed, like: The exploit mitigations to prevent you from getting an initial foothold. The sandboxing preventing you from going from a low-privileged to a privileged process. The permissions model preventing unauthorized camera access in the first place. The kernel hardening to stop you from poking at the co-processor registers. etc. etc. If all those things have failed, the last thing to at least give you a chance of noticing the compromise, that's that LED. And that's why it stays on for 3 seconds, all to increase the chances of you noticing something is off. But things had to have gone pretty sideways before that particular hail-mary kicks in.