Lawmakers unlike other branches of goverment cant act upon their interests at any given moment. For example, if a Lawmaker had stock in google he cant simply choose to have a case where google is found to be "correct", he is assigned the case and this is where we can simply prevent this specific lawmaker of handling this case. As long as a lawmakers stocks are made public and i known, we can simply prevent them from pulling strings before they even get to the case.