They don't have inventory/consumables which makes money laundering easier. The low transaction cost makes paying cash normal. The primary cost is labor and they force the indentured employees to pay it back for 'living expenses'.
Your point sounds sound other than the overt insinuation that its all rooted in fraud.
Money laundering taken as a whole is estimated to be the fifth largest economy in the world. Bigger than Germany’s. He’s not wrong.
IIRC in the UK specifically it's the biggest export industry. It's why the City of London (not to be confused with the city that is called London) won't ever be broken up.