I think we agree that individual humans are driven by a diverse set of incentives and motivations, some of which cause the pursuit financial gain, but many of which do not.
It seems that you are saying that a public company is an entity that purely seeks financial gain (at least, as its meta-objective -- e.g. it may take actions that it believes will increase profits in a rather indirect way, with direct monetary loss initially), and that non-monetary incentives are not a meaningful factor. Please correct me if I don't have that right.
Public companies are made up of people, so if your above argument is to hold, it requires that the non-monetary incentives driving those individuals are _utterly and completely_ suppressed, at least for any actions and decisions related to their work.
I can believe that the non-monetary incentives are _heavily_ suppressed by the company, but I don't think this suppression is so utterly effective such that those incentives should be entirely disregarded. I'm not sure how much weight we should place on these other factors, but it certainly seems that it usually won't be 0.
If this is done taking into account all available information, no info is ignored, no info is hidden, then there is nothing more to say. The CEO has done their job.
There is no mandate for a business to be ethical, moral unless this is considered to be in the best interest of the shareholders. Is FB value going up or down if FB decides to be moral and ethical towards the users? That answers the question "why are only some companies moral".
Apple for example decided to take the high road and be the champion of user privacy because they failed to compete with FB, Google, and the likes in the battle for users' data. So adopting a "moral/ethical" position opposing others was the way to bring value to the company.
Companies are not people. Decisions are driven by profit whether in the short or long term.
Edit: leaving ethics out of this.
Edit: to address the parent edit to remove “ethics” and distinguish “morals” for different treatment, the division of subjective preferences into “ethics” and “morals" (and “aesthetics”, for that matter) is fairly arbitrary and subjective in any case.
When the law forbids what people don't consider wrong, it becomes tyranny.
I don't think that's entirely true; legal codes often specify things on which there is a strong preference for uniformity (or benefits which can only be gained by uniformity) but where the details of the uniform rules are not themselves a near-universal consensus independent of the law. I don't think this makes them bad legal codes. (Prohibiting driving on the left-hand side of a public roadway in the direction of travel, for instance.)