Roy penalties are administered by the O police, for example prison. O penalties work better when resources are scarce. In a boom resources can also become scarce, companies might commit fraud if the fines and loss of business because of their reputation is are less than the profits.
While the Y-V companies can make the lion's share of profits much of the fraud was driven in Iv-B, dishonest subprime salesmen falsified loan documents that in many cases were already liar loans. The fraud escalated between these two and often the Y-V companies believed these loan documents were true, also Bi pension funds bought subprime bonds based on them.