That was my thought as well. High denomination notes used in the underground economy essentially represent a zero interest loan to the currency issuer. The Uni

That was my thought as well. High denomination notes used in the underground economy essentially represent a zero interest loan to the currency issuer. The United States actually considered reissuing the $1000 bill since the $100 greenbacks were losing criminal market share to the Euro. Any major money laundering is done via asset purchases, primarily using banks in the City, the Caribbean, and (for the VIP Platinum Club Elite oligarchs) Luxembourg. So money laundering is an excuse to ban high denomination cash transactions. The question is why.