Why does a line segment have only one perpendicular bisector?

A line segment has only one perpendicular bisector because the bisector is defined as a line that divides the segment into two equal parts at a right angle. For any given line segment, there is a unique midpoint where the segment can be divided, and the perpendicular line drawn through this point will always intersect the segment at a 90-degree angle. Since the properties of Euclidean geometry dictate that a line can only intersect another line at one point, this results in a single perpendicular bisector for the segment.