Why did James Beattie reject the idea that music mainly imitates things?

In his 1776 work, Essay on Poetry and Music as They Affect the Mind, James Beattie rejected the prevailing 18th-century view that music is primarily a representational or imitative art form.1

During this period, many theorists—most notably Charles Batteux—argued that the fundamental purpose of all fine arts was the "imitation of beautiful nature". Beattie challenged this by asserting that imitation is not the source of musical excellence. Instead, he argued that expression is the true foundation of music. By prioritizing the capacity of music to convey and evoke human emotion over the attempt to mimic external objects or sounds, Beattie helped shift the focus of aesthetics toward the theory of art as emotional expression, a perspective that would later be widely adopted and further developed by the German Romantics.1