Why did Artemis become a goddess?

No, she was just associated with Selene the real moon goddess. It is said that she drove the moon chariot when it was a crescent moon. Another moon goddess was Hecate. Artemis, Selene, and Hecate made the Triple Goddesses of the moon. Artemis was the crescent moon, Hecate was the new moon and the dark side of the moon, and Selene was everything else.