Scared people legislate all sorts of things to allay their fears.
IIRC, one of the reasons for the threaded barrel thing, was from initially banning flash hiders. Yep. The ubiquitous $10 A2 birdcage, that many evil rifles were shipped with.
Some scaredy cat went, "Oh no! Those evil flash hiders will mean no one can pinpoint the location of the evil shooter doing evil things at night!".
Similar reason for why the UFC allows elbows, but not spiking elbows (elbows thrown at a downward angle, striking with the point of the elbow with the forearm perpendicular to the surface/body part being struck).
One of the folks in charge of the regulations saw a demo at a martial arts event, where a person did the multiple ice block break with a spiking elbow, and thought, "OMG... that's too dangerous to allow", not understanding that what they call slashing elbows (where the forearm is almost parallel to the point of impact) can actually deliver even more force than spiking elbows. But something scared someone, therefore, it needed to be banned
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