It is accepted that governments (Parliament) established central banks and gave them the special power to create money. Because of this special power, central banks have a great responsibility, and that is to protect the value of the currency (that is, to keep inflation low).
The monetary policies needed to keep inflation low, are often very unpopular, and politicians normally do not like to take responsibility for such unpopular measures. Furthermore, the power to create money can easily be abused for short-term gains, but any excessive creation of money in the short-term will eventually lead to higher inflation (and therefore higher interest rates).