Mary Jo White isn't a banker, she's a securities lawyer. She was a big deal partner at a major law firm before she went to the SEC. She's almost certainly going to go back to the same job after. All her incentives are aligned with aggressive enforcement of securities laws. Her firm makes money when the SEC comes down on people, not when it rolls over and lets things slide. You can see this starkly in the antitrust world. There was a lot more money in antitrust practice back before the current trend of going easy on antitrust enforcement.