money laundering

maam I don’t understand why ML is easier in case of cash-intense businesses than in case of credit based businesses?

Say a CEO shows that the revenue has been generated by legitimate sources (when in fact part of revenue has been generated from illegal activities) then the proceeds will get into the books. at least the auditor would want to see it in cash flow form operations and also spot in the bank statement provided by the bank, so then how can the CEO route it outside the company when the cash proceeds are reflected in SPL, SCF and bank statement?