Well I’m glad you asked! Because “Maris” doesn’t mean “Mary.” It means “sea” or “ocean.” So the title literally means, if you keep the same word order: “Hail, Sea Star.” So where did that wording come from?
The original lyrics date back to somewhere around the 9th century and have been attributed to several authors; no final conclusion has been reached on that issue. The words present Mary as a merciful and loving mother, with “Star of the Sea” being a title that especially appealed to travelers praying for a safe journey. The words were sung to Gregorian chant music, which is always anonymous.