Why did Michael Collins stay aboard the command module?

Michael Collins stayed aboard the command module during the Apollo 11 moon landing in order to maintain communication with both the lunar module and Mission Control on Earth. His role was crucial for ensuring the safety and coordination of the mission while Neil Armstrong and Buzz Aldrin explored the lunar surface. Collins operated the command module, ensuring it remained in orbit and ready to return to the lunar module for the journey back to Earth. His presence was vital for the success of the entire mission, even though he did not walk on the moon himself.