Why is conventional current shown in the direction opposite to electron motion in a metal wire?

In the study of electric current, the convention of defining current direction as opposite to the flow of electrons is a historical legacy.

In the 18th century, Benjamin Franklin proposed that electricity was a single fluid that moved from positive to negative charges. Although we now know that the primary charge carriers in metal wires are negatively charged electrons moving in the opposite direction, the original definition remains the standard in electrical engineering and physics.1

This is known as conventional current. By definition, current is considered positive in the direction of positive charge flow. Because a flow of negative charge (electrons) in one direction is mathematically equivalent to a flow of positive charge in the opposite direction, this convention allows for consistent calculations across various media, including semiconductors, where both positive "holes" and negative electrons contribute to the total current.21