Why does your film need a "Color Conversion"? Because cinema projection is a completely different optical environment.
You graded your film on a monitor in a room with lights on. Your screen creates colors by mixing Red, Green, and Blue (RGB) light.
DCP software translates your specific RGB values into XYZ—a universal language that describes "color" mathematically, not just "light pixels."
Theaters are pitch black. Projectors use a wider palette (P3) and darker shadows (Gamma 2.6). Without conversion, your film looks wrong.