Criminals performing illicit activities prefer to use cash as their main financial instrument to facilitate their transactions. Given its anonymity and privacy, authorities around the world faces difficulty in tracking criminals down. However, cash has it drawbacks. The smaller the denomination of the cash collect can amount to a heavier weight, which requires more logistical planning.
This is why many countries around the world are slowly discontinuing their largest notes. The main purpose is to further inconvenience criminals that deal with cash. In 2014, Singapore has discontinued its $10,000 note, giving the Central Bank of Singapore a boost in its anti-money laundering / countering the financing of terrorism regime.