Organizations that provide financial services cannot afford to have its employees leave their morals on the front door when they step inside. Finance usually depends on a very high level of ethics.
Markets break down without trust. If financial markets are full of rogue traders, individuals will start to disengage from it, thereby reducing the capacity to find investments and hence reducing the economic growth. A market with strong ethics is more inclusive which helps it to be more liquid and offer cheaper financial options.
Financial market participants often have economic freedom, and often with good reason, but the successful financial exchanges in the world are more famous for trust than the degree of their freedom.
If trust is important and if it cannot be achieved by laws alone, how important is it to have agreements and moral codes that are beyond the law, especially when the law is often the way to codify the ethical behaviors?