Call them Too Big to Behave—banks that are so big the people running them know virtually nothing they do will get their institutions run out of business or their executives prosecuted.

A New York Times analysis of Securities and Exchange Commission enforcement actions found at least 51 cases in which Wall Street firms had broken antifraud laws over the last 15 years that they'd pledged in earlier settlements never to breach. Those cases involved 19 firms, including nearly all the megabanks: JPMorgan Chase (JPM), Bank of America (BAC), Goldman Sachs (GS) and Morgan Stanley (MS) among them. Despite the repeat offenses, the SEC issued at least 344 waivers from sanctions that would have curtailed the banks' activities, the Times found.