Defences against a standing strangle with the hands AKA 'rape choke' are very commonly practised in self-defence classes yet when I roll with people in BJJ classes nobody ever seems to try it on me. Why is this?
Choking with hands wrapped around the throat is not efficient
The goal of chokes in BJJ and judo is to cut off blood to the head at the carotid arteries and jugular veins, which can render a person unconscious in seconds. Cutting off air takes much longer, so blood is strongly preferred. If you are trying to do this with each hand squeezing on both sides of the neck, you have two problems:
- You are relying on your hand strength only to apply force to the blood vessels. Direct force from the arms will be into the windpipe, which is not where you want it.
- The force applied by your hands is spread over your fingers, reducing pressure on the blood vessels. It does not help to cut off the blood in more than one place; to cut off blood, it is sufficient to have maximum pressure in one place.
Choking with your hands wrapped around the throat is not efficient because your hands are weaker than your arms and body. There are much better options like cross chokes, the rear naked choke, or even choking with knuckles directly on the blood vessels.
Contrast choking with hands wrapped around the throat with:
- A gi cross choke. You apply pressure to the blood vessels with the small area of your wrist or forearm. You get leverage from scissoring your arms when applying the choke. Your arms are much stronger than your hands. All of this adds up to much stronger choke.
- Choking with knuckles directly on blood vessels (ryote jime)[thanks to Philip Klöcking]. By using the knuckles instead of the surface of the fingers, the pressure on the blood vessels increases. You can adjust the angle of your arms to directly apply pressure on the blood vessels, either with your arms, or ideally with your body weight.
(A bit of a frame-inversion here - I'm answering "why do we learn this if it's not useful when we roll" instead of "why don't people do this when we roll")
This is typically not being taught as a defense against a "trained" opponent, nor a "sports" defense for rolling with people in class or tournaments.
This is often being taught as "combat" self-defense against an opponent (usually untrained) who is intending you serious harm. For example, as you said, "rape choke".
Martial Arts originated as self-defense, not as a sport, and as such some techniques you learn will fit in one of those buckets but scarcely feature in the other.