Risk Management Plan as Input

Please clarify why is the Risk management plan an input with the same name in the following processes of Risk management while the other knowledge areas has shown such plans as part of the overall project management plan as input. 

For example cost management plan, communication management plan, quality management plan in planning etc.. when they are input in executing/monitoring process they are input as overall project management plan except this knowledge area where in except in M & C process it's input as risk management plan?

Are there any specific reasons for this?