Why was Tyrian purple associated with rulers and high priests?

Tyrian purple was associated with rulers and high priests primarily because it was an extremely costly dye to produce. Derived from the secretions of specific shellfish, such as Bolinus brandaris, the process of extracting the color-producing substance was labor-intensive and expensive.1

Because of this high cost, garments dyed with Tyrian purple became a distinct mark of imperial or royal rank, leading to the expression "born in the purple" to describe those of noble birth. This association with prestige and authority extended into religious contexts as well; for instance, in the Roman Catholic Church, the phrase "promotion to the purple" signifies an elevation to the rank of cardinal. Its status as the most celebrated color of antiquity ensured that it remained a symbol of power and high office for centuries.1