Why Procurment negotiation is not a T&T in control procurement , while we always negotiate with our customer during M&C process

Procurement negotiations are performed in the execution phase, under Conduct Procurements. The T&T's include bidder conferences, expert judgement, and "procurement negotiations" among others. Control Procurements is more about monitoring and control of procurements. When involved in the T&T's of the Control Procurement process, such as performance reviews, claims administration etc., you are indeed correct, procurement negotiations may follow again, BUT this would be happening under Conduct Procurements, even if it is a result of Control Procurements. Thus the iterative nature of these processes. When, as you say, you are negotiating procurements T&T with your customers during the M&C process group, you are in fact performing the Conduct Procurement process inside the Execution Group, in tandem with Control Procurements inside the M&C group.