Why did Greek astronomers conclude that the heavens were made up of perfect crystalline spheres moving at constant speeds?

Greek astronomers, influenced by philosophical ideals, believed that the heavens were perfect and immutable, which led them to conclude that celestial bodies moved within crystalline spheres. This concept was rooted in the notion of perfection associated with geometric shapes, particularly circles, which were viewed as the most perfect form. The idea of constant speeds reflected their observations of celestial motion, as planets and stars appeared to follow regular, predictable paths across the sky. Consequently, the combination of philosophical beliefs and observational consistency shaped their view of the cosmos.