Why do we need WMS software on top of ERP?

Why do we need WMS software on top of ERP?
Why do we need WMS over ERP

Enterprise Resource Planning and Warehouse Management System are the backbone systems to any distribution center, wholesale, supply chain or FMCG business. Without them, these businesses wouldn’t be able to function. What is ERP software? Enterprise Resource Planning (ERP) is a business management software that integrates key areas and automates business processes across all departments of an organization