The problem is that frauds are fat-tailed. The vast mayority of them are small, but most harm comes not from them but few huge ones where there is no economy of

The problem is that frauds are fat-tailed. The vast mayority of them are small, but most harm comes not from them but few huge ones where there is no economy of scale to offset it. If one increases the number of transactions, then it can be depending on fraud distribution details that harm from big ones increases disproportionately and makes average cost of transaction higher.