Why does people sway side to side if sitting still?

People may sway side to side while sitting still due to a natural tendency to maintain balance and stability. This subtle movement can be a subconscious response to adjust posture or distribute weight evenly, especially if they are relaxed or not fully engaged. Additionally, it can be influenced by factors such as muscle tension, restlessness, or even the body's vestibular system reacting to a lack of external visual cues.