The use of money has evolved through history and FIAT money is just one of the last evolutionary phase of money.
"Representative money has now been replaced by fiat money. Fiat is the Latin word for "let it be done." Money is now given value by a government fiat or decree. In other words, enforceable legal tender laws were made. By law, the refusal of "legal tender" money in favor of some other form of payment is illegal."
Through FIAT money the government exercised its power and planned development of the economy and of course manipulates the market.
It is obvious that it will never give up the resource in achieving the rule over the population.
FIAT money is not necessary, and it is mainly the source of many accidents in the economy, but as I said, how can someone give up the greatest tool of control.