Why are most word sounds arbitrarily related to their meanings?

In the study of semantics, the relationship between a word's sound and its meaning is considered "arbitrary" because the vast majority of words do not possess a direct, natural connection to the objects, processes, or qualities they represent.1

Vocabulary must be largely arbitrary because the greater part of human experience and the world itself is not inherently associated with specific noises, gestures, or physical shapes. If word sounds were naturally linked to their meanings, languages across the world would be much more similar to one another. Instead, different languages use entirely different labels—such as horse, Pferd, cheval, and hippos—to refer to the same animal, demonstrating that these associations are established by convention within each specific language community.1

While some exceptions exist, such as onomatopoeic words that mimic sounds or instances of sound symbolism where certain sounds evoke specific tactile or visual qualities, these represent only a very small fraction of any language's total vocabulary. Ultimately, words function as symbols that are related to their referents only through social convention.12