Why is there a black mask around raccoons' eyes?

Raccoons have marks around their eyes. It's just a natural thing to happen. If you have brown hair, that's just like saying "Why do you have brown hair?" Or "Why do you have eyes?" But robbers/burgalars have a mask around their eyes to imitate raccoons. Raccoons steal things out of people garbages. There's no REAL reason why raccoons have the marks around their eyes.