"Thompson easily won convictions for possession of moonshine, but Judge Gray was lenient in sentencing, rarely doling out jail time.
"It was a game," said Merritt, the former U.S. attorney. "Gray didn't like these cases. He thought they were a waste of time, and he was right."

They say this is a decades old tradition, but it is really a millenia old tradition.
Remember the Shays Whiskey Rebellion? George Washington went after them because they wouldn't pay taxes, not because they were moonshinin' ! He was a smart, rational, practical man.

It's easy to go after the criminal on the street (hence the popularity of shows such as 'Cops')
Much more complex and difficult to go after corporate crime.