That is the difference between something being firmware controlled and hardwired.
And for new macs the off switch for microphone/mic if the lid is closed is hard wired using some "dump circuit logic switch" AFIK.
The problem with lights (even if hard wired) is that you might still find ways to brake them, like finding a way to fry them without braking the camera or switching on/off so fast that it isn't really visible but you still get some image/sound you might be able to post process to a point where it's usable even if not grate. You probably can prevent this with further hard wired circuits, like a hard wired "super slow de-bouncer" which in a on-1->off-2->on makes sure 2 is prevented if not at least Xs passed since 1. And which in a off-2->on-3->off cycle makes sure the LED is on for at least Ys (the camera can be switched off faster, just not on again). But I don't think apple has something like that. At that points the question is why not put in physical switches like e.g. on Framework laptops or some older ThinkPads.
Probably, if you hacked a device to a point you have root access or worse it's not that uncommon that you are able to reflash firmware to custom firmware.
A lot of firmware, and firmware signature validation, is ... not very well done.
Practically it's often not worth it (you already had root+ access. It's doable, but not simple and less uniform applicable.).
But there have been known cases of viruses tryign to persist themself in the firmware of connected devices (which in this context includes all internal devices including the motherboard).
