Why do you have marketing managers?

A Marketing Manager will be necessary for various tasks based on the size of one's business entity (or organization, company, etc).

For smaller entities a Marketing Manager may handle all the aspects of the marketing cycle for the said entity. For instance, determining demographic targets, analyzing market trends or needs, ensuring company recognizeability amidst said demographic, and etc.

For larger entities a Marketing Manager may be needed to do a specific task for said organization. The macromarketing duties may be in the hands of a Vice President who delegates various projects or sectors to each Marketing Manager.