Why is the trio section of a minuet and trio often in a different key?

In the context of ternary form, the trio section of a minuet is typically composed in a different key to provide musical contrast and variety.12

In Western tonal music, modulation—the process of changing from one key to another—is a fundamental resource used to create interest and tension. Because the minuet and trio structure follows an aba pattern, the trio serves as the middle section that departs from the home key of the initial minuet. This shift in tonality, often to a closely related key, allows the composer to introduce a new harmonic color before the return of the original minuet section, which restores unity to the movement.3241