I think the clear distinction here is between advocating for something and passively watching. Sanctioned suicide isn't advocating for people to commit suicide, it's supporting those that have already made the decision. Watchpeopledie is also passively watching death, not advocating or trying to incite death.

The clear difference in u/magnora7's judgement of these three subs is right in his post:

Neither openly advocate violence

Please notice neither ADVOCATE violence, meaning none call for others to commit violent acts. From what he said, s/PhysicalRemoval was openly calling for violent acts. I don't really see how there's confusion here, he said it pretty clearly already...