That's because there are already conflict of interest laws on the books for Congress. Those laws, however, did not include the Executive branch.
Lucky for Congress, Blatant Conflict of Interest Is Still Perfectly Legal
http://www.theatlantic.com/politics/archive/2012/10/lucky-congress-blatant-conflict-interest-still-perfectly-legal/322790/While insider trading is banned in Congress, it's still completely legal for lawmakers to sponsor bills that could benefit the businesses and industries or their family members have invested in, and according to The Washington Post, 73 congressmen and women have figured out how to use this loophole—a jump from the 16 they found when they published this study in February. In March, Congress passed a ban on insider trading after being embarrassed by 60 Minutes last November on the ways members had taken advantage of their information to trade stock on hot legislative tips. President Obama gave the practice mention in his State of the Union, and after some protests from members, some new rules went into effect like requirements to disclose stocks purchased on the Internet.
So no more sneaky legislators financially benefiting from legislation! Now, as The Washington Post's team of Kimberly Kindy, David Fallis, and Scott Higham explain, it's all about legislators blatantly benefiting from legislation. Due to the remaining loopholes, to name just one example, Rep. Mike Kelly, a Republican of Pennsylvania, was allowed to sponsor a natural gas bill the same month Exxon negotiated a multimillion-dollar deal with his wife. Across the aisle, former Rep. Dennis Cardozo, Democrat of California, helped pass a bill that involved tax breaks for racehorses and was then bought seven such racehorses when the new tax breaks came into effect.