I also like this clip. This is how I like to think of kata-dori. Pay particular attention to how he says not to use the hand, but to use the shoulder to move uke.
Why is this harder in jutai or ryutai?
My observations from practice: Itīs particulary in jutai. When you speed things up most people starts going backwards instead and/or forgets to drop & rotate to get under uke. I personally havent met that many that can do that waza smooth and correct in jutai.
In ryutai itīs pretty common to not let uke get the grab and the waza becomes more like ai hanmi katatedori (or kosa dori if you like).