The main reason is a principle in international finance theory 'impossible trinity', which means that a country must give up one of the three goals (Manetary independence, Full financial integration and Stability of currency) due to factors of economic power. These three goals

They cannot be achieved at the same time. Developed countries generally give up interest rate stability to obtain monetary independence and full financial integration. Developing countries generally choose to maintain exchange rate stability (stability of currency) and full financial integration, which results in a reduced role of financial policy (Manetary indenpendence).

Before discussing this issue, we need to distinguish between two main methods of fixing exchange rates. Taking the US dollar as an example, one is called the 'currency board' - that is, the central bank must ensure that there is a US dollar in foreign exchange reserves before it commits to issue one unit of national currency.

into a central bank, the other is called 'dollarization' - both using the US dollar as the country's official currency.