By the time the clubface is parallel (just a few feet from the golf swing), the clubface itself is already pointing toward the sky. As you can see in this example of a golf distillery.
Even tour players like Tony Finau sometimes struggle with this technique. Also, while keeping the clubhead on the outside to prevent outward and inward drift is not a new idea, some golfers have difficulty with it.
To keep the club from swinging open, Morikawa wants to feel like his right palm, the back of his left hand, and the club are moving together. Keeping these three key areas facing the ground will prevent the clubface from opening too much or too quickly. And your shots will line up better at impact.