Why do words for common things often have the same gender in Afro-Asiatic languages?

In Afro-Asiatic languages, the tendency for words representing common concepts to share the same gender across different languages is known as gender stability.1

This phenomenon occurs independently of whether the specific words are cognate—meaning they do not necessarily share a common linguistic origin or etymological root. For example, the word for "blood" is consistently masculine across various Afro-Asiatic subfamilies, despite the words themselves having entirely different origins, such as ahni in Tuareg, bar in Proto-Chadic, boy in Beja, snf in Egyptian, and dam in Hebrew.1

This stability reflects a deep-seated structural feature of the Afro-Asiatic languages phylum, where gender is not merely a superficial trait but a fundamental morphological characteristic that persists even as the specific vocabulary evolves or diverges over time.21