Prosecutors, as with all predator classes, choose their targets carefully so as not to both expend unrewarding effort and avoid self-injury.
Unfortunately, this means often foregoing large and egregious targets, such as the organised criminal syndicate known as United Healthcare, in favour of far smaller, and more tractable, targets. This has always been the case, and is hardly limited to the United States.
Finding ways to remedy this fundamental systemic dysfunction would be greatly appreciated.
(The observation in my first 'graph isn't a sneer or slight at prosecutors, though some of those might also be deserved. It's a recognition of the nature of the activity.)