A death threat is something like saying "I'm gonna murder spez". It expresses an intention. An illustration suggesting that someone could be killed does not express any intention to actually kill someone. Furthermore the image could be interpreted in other ways, like saying the user account "spez" should be eliminated, or that that spez is the kind of person who would have been killed had he been around in the French revolutionary period. No reasonable person could believe the people posting those pixels are actually making plans to cut off Steve Huffman's head with a guillotine.

I'm much more concerned about rhetoric that, for example, equates LGBT+ people with groomers, because that shit demonstrably does get people killed, and I've been told numerous times that rhetoric like that doesn't violate any rules. If moderation is dead, that's what killed it.