Why did Copernicus still need epicycles in his model of the solar system?

Nicolaus Copernicus retained epicycles in his heliocentric model primarily because he maintained the long-standing philosophical commitment to the principle that all planetary motion must be composed of uniform circular motions.1

While Copernicus successfully placed the Sun at the center of the solar system, he did not yet recognize that planets move in elliptical orbits. Because he insisted that celestial bodies move at a constant speed along perfect circles, his model could not accurately account for the observed variations in planetary speed and distance without the use of additional mechanisms. Consequently, he employed epicycles—small circles whose centers moved along larger circular paths—as a mathematical tool to approximate these noncircular, varying motions. In this context, these epicycles functioned similarly to terms in a Fourier series, allowing him to refine his model's accuracy to match observational data while adhering to the traditional requirement for uniform circular motion.123