If marking menus are more efficient than linear menus, why haven’t they been adopted?

In User learning and performance with marking menus by Kurtenbach and Buxton (1994), the paper demonstrates that marking menus are more efficient than linear menus. And to me they look just as intuitive.

What are the reasons they have not been adopted by the industry? if not for the general public, I would think that power-users enjoy more efficiency.

Here is a summary of the paper.