They want to be able to buy one package that does everything from keep track of sales orders, to payroll, to manage inventory, to spit out their end of fiscal year tax return and SAP is trying to fill that need. However, it is impossible for SAP s programmers to design software that covers the needs of every single large business. Every business is different. They manufacture different products. Their employees have different titles.
Inventory control is quite different for cars than gasoline, for bushels of corn than software.
Therefore, every package must be extensively adapted to each client. And since businesses are not static, they change, the software will not stay the same for long. It must be tweaked, revised, cut and expanded to meet the ongoing needs of the business. Actually working with the software as it stands, and developing applications for your particular business. ABAP is the programming language used to make those changes to the packages.