The hijab, veil, burka etc. are the “slave uniforms” for Muslim women. It shows that she is the slave to some Muslim man’s will. It allows any Muslim man who knows her to keep tabs on her in public, and rat her out to her husband/father/slave owner if she tries to step out of their control by removing her slave uniform.
Sometimes the most important reason they require women to wear the hijab is so the men have a way to disguise themselves as women when losing a fight.