Grip shift is not the most natural and intuitive way to control shifting. Have you ever tried to teach someone how to ride a bike and not tell them how the shifter works?

They magically just know how it works? No. The control mapping is not necessairly obvious and it is not intuitive which way the shifter is supposed to turn to produce the desired effect.

Just because it is intuitive to you, because you've used it doesn't mean it actually is to others.

Someone needs to do a design and usability analysis on these things.