[galaxyLogic]

If creating furniture was physically as easy as writing software, I think many people would create their own furniture, just to create a chair that fits them exactly.

Similarly in software there is not "one size that perfectly fits everybody". Therefore there is much need for customization.

When you write software you are in effect not only creating the program. You are creating a system that consists of the computer, its program, and its user. The way the task is divided between what the human does and what the computer does can be done in very many ways. In some systems that results in a system where users need to do more but thus also have more options for controlling the system. Therefore there are so many different ways any "applications" can be written.

No program is an island. It is something that must interact with its users. It is always designed to be a part of a bigger system consisting of itself and its users.