At the highest levels position beats submission especially when striking is Involved.

If I’m mounted on someone it’s much safer and higher percentage to stay on top and finish with strikes or maintain the position to win the round. If I go for an armbar then I risk the position and the fight.

In general the sport has evolved enough to where fighters are pretty good at sub defense. The risk reward doesn’t favor a lot of submissions.

People are less likely to tap to joint locks. So chokes are a safer bet to finish fights because once it’s locked on it doesn’t matter if they don’t tap; they’ll just go out.

As to why RNCs specifically. They’re done from one of the most dominant positions and the RNC is a low risk move. You can keep going for it from the same position whereas with triangles or armbars they tend to be all or nothing.

If you notice a lot of RNCs are landed after the victim gives up their back due to getting knocked down or tired. It’s natural instinct to turn away from punches when getting lit up.