Why Singapore runs monetary policy through the exchange rate and not an interest rate

Background

The Monetary Authority of Singapore (MAS) is Singapore's central bank. MAS states that it "conducts monetary policy to maintain price stability conducive to sustainable growth of the economy" and that "this objective is enshrined in the MAS Act".
MAS states plainly that "Monetary policy in Singapore is centred on the exchange rate" and that "in the small and open Singapore economy, the exchange rate is the more effective tool for maintaining price stability".
The reason MAS gives is structural: "in a small and open economy such as Singapore, where gross exports and imports of goods and services are more than 300 percent of GDP and domestic expenditure has a high import content, the exchange rate has a much stronger influence on inflation than the interest rate".
Accordingly the framework is "centred on managing the Singapore dollar against a trade-weighted basket of currencies", known as the Singapore dollar nominal effective exchange rate (S$NEER).
The S$NEER is "MAS' intermediate target of monetary policy" and is "kept within the boundaries of the policy band".
"The primary tool for managing the S$NEER is intervention operations in the spot foreign exchange (FX) market." These involve "the sale or purchase of US$ against the S$", the most liquid Singapore dollar currency pair traded.
Because MAS buys and sells foreign currency to hold the band, the implementation of policy itself makes MAS "accumulate or expend Official Foreign Reserves (OFR)", changing the size of its balance sheet. MAS therefore does not announce a policy interest rate the way most central banks do.