Why does a single organization have many different types of database configurations. What would be t

why does a single organization have many different types of database configurations.
What would be the value of having multiple configurations.

Most often that's the result of growth and time. Very seldom does an organization set up an entire system at the same time. They start out in one area, then add another system somewhere else. Meanwhile the technology is changing so the next job gets the new stuff. Often the programmer that did the original system is no longer available and the new people use a different system. In sizeable, growing systems, that's almost always a problem unless they change everything at once and that's often a very expensive process. It can also be risky if they change to something that doesn't work.