Trope seems to spread very little, having only 32 Wicks and 42 inbounds, despite being a widespread trope and not too recent (Launched in early March). The below reasons may be contributing factors to this.
The trope is broader than the title implies: The trope is about a robot's head being what houses its vital processing units, and in many cases is all the robot needs to remain functional, regardless of whether this is actually exploited as a weak point.
About half of the (clearly described) wicks seem to be about robots getting shot in the head. This is not strictly misuse, but suggests some people are taking the title literally.
The current title describes the trope in the sense that if a robot's "brains" are stored in its head, receiving a headshot will logically kill it.
The other half of the wicks have nothing to do with robots being shot in the head, instead mentioning robots whose "brains" are located there, which is the definition of the trope.
32 wicks is a perfectly healthy level of wicks for most tropes.