From the "Why Experiment with Initiative?" section:
The initiative rules in D&D work very well. They keep the action moving and are easy to use at the table. In terms of design, fifth edition’s approach was to treat initiative as an element of the game that was meant to produce as little friction and complexity as possible.
The Greyhawk initiative variant takes a different approach. These rules add complexity, but with the goal of introducing more drama to combat. The order of actions changes during combat, making it impossible to depend on creatures acting in a consistent pattern. Moreover, this initiative system requires a certain amount of strategizing between players ahead of each round’s action.