Central banks are independent so that they can better focus on their goals without interference from others and for a longer period of time than is often the case with, for example, the length of politicians' terms in office. This is believed to contribute to greater stability in the economy, among other things.
The Government has often decided by law that certain institutions are responsible for specific and limited tasks and also have the independence to carry them out.
This is considered a more suitable arrangement than, for example, politicians making decisions for these institutions, as has been the case in some places before. One of the clearest examples of independent institutions of this kind are the courts.
In the case of central banks, it has been considered inappropriate for politicians to make decisions about interest rates, for example. They might be tempted to keep interest rates as low as possible before the election but raise them after the election to respond to inflation. This could contribute to higher inflation and instability in the long term. Therefore, central bank governors, various other officials, and people who make important decisions are often appointed for a term longer than the politicians' term. This arrangement is believed to contribute to greater stability in the economy and society in general.