There are two main reasons why this is likely to be true.
First, this is likely to be true because those who are lower on the corporate ladder feel more of a desperate need to compete in order to move up the ladder. They likely feel that they cannot afford to follow the codes of ethics for fear they will not be promoted. They might feel that they are, at least implicitly, being pressured to violate the codes of ethics by their supervisors and managers. This can make them cynical and hostile.
Second, it may be that the people on the lower rungs of the ladder feel that those above them routinely violate the codes of ethics. They may feel that the higher-ups pay lip service to the codes of ethics but do not take them at all seriously.
The best way for top managers to change this view is to be aggressively transparent about their actions and their expectations. They have to make it very clear that their actions are all in accordance with the ethical codes. They have to make it very clear that they will not promote those who do violate the codes. If they can do these things, the people lower down the ladder will likely be less cynical and hostile to codes of ethics.