Corporations are treated under the law (in the U.S. and many other countries) roughly as if they were human beings. They can own things, they can be held to have broken the law and fined accordingly, etc. Economists mostly expect them to act as if they were human beings, and pursue their own self-interest (since most economists believe actual human beings pursue their own self-interest). This is mostly how even the detractors of corporations think; when they accuse corporations of being greedy or evil, they are applying human psychology to a corporation. Everyone knows that they are not actually humans, but both law and normal reasoning thinks about them as if they were.
The problem with this is that they, quite literally, have no shame. Human beings have shame, pride, a concern with reputation, a concern for retirement, etc. Humans do sometimes decide not to do something because it is illegal, and we fear the consequences of being arrested, but not least among those consequences are the shame of being put in jail, pictures taken of us for a mug shot, other people being told what we did wrong, etc. When people are breaking a law they feel is unjust, and expect to go to jail for it, they behave very differently (because they are proud, not ashamed, of their actions).
Milgram and others have demonstrated that, when they are doing the job they were told to do, people don't associate themselves with the moral decision of whether or not to do it. Quite literally, they have no shame (or at least it doesn't impact their actions). Others besides Milgram have demonstrated this, including the perpetrator of the "fast food restaurant phone scam" (fictionalized in the movie 'Compliance'). Corporations are composed of people, but when acting as part of a corporation, the capacity of people to feel shame is dramatically impaired.
Reputation is, for a corporation, a job for the marketing department, to change. In other words, it is bought, like any other raw input, with money, not actions. Individual human beings build and preserve a reputation by doing what they feel is right, and avoiding that which is shameful. Corporations just buy reputation (via advertising, lobbying, charitable contributions, etc), whenever they find the lack of it to be a problem. Thus, reputation/shame does not impact the behavior of corporations in the same way that it does individual human beings.
Moreover, neither the management nor the shareholders expect to be around for the long term, so they have little reason to concern themselves with long term consequences. Even if the long-term cost to the corporation's reputation is more (in $ terms) than the gain from doing something disreputable, if it gooses the stock price in the short term then the CxO's who decided on the disreputable action can cash out their stock options and be gone before the bill (in bad reputation) comes due.
Worst of all, in a manner similar to what Dictator Game experiments with graduate economics students show, the management of corporations have been taught that they should NOT think about anything other than money when making decisions. The people who become corporate decision makers may be, as a group, naturally less disposed to feel shame for their actions, but making matters worse is that they have been taught that they are not to take into account anything other than money in their decisions.
This would be fine if every way in which we desire pro-social behavior from corporations involved financial incentives and disincentives. The reality, however, is that the financial penalties (fines, etc.) from polluting the environment, clogging the legal system with patent litigation as a way of quashing competition, devising ever more elaborate (and fragile) financial bubbles, ignoring safety concerns, etc, are never as great as the potential gains from this disreputable behavior. An individual human, acting on their own behalf, would be unlikely to behave this way. A few sociopaths will, but most people will not, and for this reason the rest of us can identify (and handle) the few for whom shame has no sting. Among corporations, though, sociopathy is the prescribed norm, not the deviation. It has become increasingly clear in recent decades that we have no handle on corporate misbehavior.
However, society (including government) has not tailored law and punishments to cater to what corporations DO care about: being broken up. One thing that people at the top of a corporation (or really any hierarchy) vehemently dislike, is having their sphere of influence reduced. A breakup doesn't necessarily cost anyone any money: shareholders get shares in every part of the breakup equal in percent to what they had before, and history shows these shares put together will end up appreciating in value at least as much as when they were all one company. If every time corporations were caught violating environmental, health, safety, accounting, or other laws, they were forced to spin off a part of the company roughly equal in value to the fine they would previously have had to pay, it would have a bigger impact on corporate activity than fines, and especially more than shame.
But for that, we would have to admit that corporations are not people, and treat them differently. Given that the current U.S. government (left, right, and center) is more or less controlled by corporations, I do not expect to see such a change any time soon.