What is the reason for not being able to use the global position?

Hello, I am a beginner and I have a question. Why is it not possible to control a drone smoothly using only the global position? Initially, I received the following answer to a similar question: ‘Since PX4 is tightly integrated with ROS2 (uORB messages are synchronized as ROS2), you are working with the internal message bus. The multicopter position controller is run through a local frame, hence the trajectory setpoint. That is why global position needs to be transformed into a local frame. You cannot use global position for trajectory setpoints, as the coordinates are defined in the local frame.’ However, my question is, why can’t we purely use the global position without converting it? Am I misunderstanding something, or is there a specific reason why this conversion is necessary? I am curious about the rationale behind this.

Can you link the original response?