I agree that it is not the payment in cash that is the problem. It is that it likely signifies that these transactions are not being reported or are being misreported (as something like cost of materials).
I doubt most of his cash payments to workers qualified as payments to independent contractors because BM controlled all the circumstances of the work - as an employer. As an employer, he should have been responsible for collecting their share of certain payroll taxes and paying his share of certain payroll taxes and insurance premiums (unemployment, workers comp) as well as reporting the amounts he paid them to the IRS.
Also, it appears he claimed these same workers as employees for the purpose of the COVID payroll protection loan.
So, they are independent contractors when BM wants to evade responsibility for payroll taxes and unemployment & workers comp premiums (which can be fairly hefty for contractors doing work involving heavy equipment and hard manual labor), but employees when the federal government is passing out free $ for employers during COVID.
ETA: BM is cheating the system. And that chaps my hide because the national debt is now over $30 trillion and honest people like me play by the rules. In a way, it is honest people like me that are unwillingly subsidizing BM’s payment of IE’s fees because, if he were playing by the rules most others honor, he’d be paying those fees out of a smaller bank account. He has more because he cheats all of us.