Despite other reasons it's probably also political. Sometimes in a high position it's actually better to not know stuff. Set up an employment contract that forces others to do illegal things in your favor but never ask what they do. When sh*t hits the fan you can exit fast, since you know you set up your guy to do bad things, and since you can access all the information that is and therefore can make smart decisions for yourself. But when the scheme gets caught on by the public your employer goes to jail, not you. Nobody ever asks for who set up the system in a way that traders feeled compelled to act dishonest.

So yes, they handed off the power to do their jobs right, but their goal was not to do their jobs right. Their goal was to make money as long as it's good and not go to jail when it's bad. And the power to do that they didn't hand of to anyone.