Why were many musical works incorrectly attributed to Joseph Haydn?

Many musical works were incorrectly attributed to Joseph Haydn primarily because he was a widely published and copied composer whose fame spread throughout Europe during his lifetime.12

As his reputation grew, aristocratic patrons and institutions across the Austrian empire, south Germany, and Italy assiduously collected his music, leading to the widespread dissemination of his works in various libraries. Because his music was so frequently copied and circulated, the authenticity of many pieces bearing his name became difficult to verify. This resulted in a staggering number of spurious attributions that persisted for many years. It was not until the 1950s that extensive musicological research began to systematically remove these incorrectly attributed works from his recognized output, a process of creating a definitive catalog that continued into the late 20th century.321