The 3 knowledge areas (KA) scope, time, and cost do not have a specific project management plan, instead they are included in the project management plan.

Other KA (quality, procurement, etc.) have a specific management plan that is an input of their different processes.

Why dont' we have the project management plan as an input of most/all all processes of the KA scope, time, and cost? The project management plan should provide guidance on the management of those differnet processes, hence should be an input.