The best way to speak about a person is symbolic language. This leads to a multitude of images attempting to capture Mary's personality. There is a third reason which deals with Mary's intercessory role. Mary's role as mother and her intimacy with her Son made her a powerful intercessor throughout Christian history. Since human needs are countless, as numerous as the varied situations and expectations of human life, Mary's help was and is sought for all of them.
Many titles are due to geographic and cultural reasons.
There were times when not only every country but also every little village wanted to have their own lady chapel or lady image. This led again to a multiplication of titles. Apparitions are often accompanied with healing and conversion. This makes it even more plausible to coin a specific title as is the case for major sites like Lourdes and Fatima.