I'm sure if the DAs could prove that any bankers had broken the law in court, they would be more than happy to prosecute them. The problem is two-fold: it's much less clear which if any laws were broken by the nebulous "bankers," and even if we knew which laws were supposedly broken, it will be harder to prove intention, which in the case of laws without strict liability (most of them), might end up making it hard to punish the person being investigated.