Because we can build a better society. Because the profit motive is an extremely powerful one, and there is simply no reason not to use it as a force for a better society.
I understand why the status quo is the way it is. I'm arguing that it can (and has to) change, not just for the betterment of society, but for the long-term health and profitability of the corporations themselves. The kind of planning needed to ensure this is not something corporations are equipped to handle, nor is it the kind of planning they can legally do.
I've been an executive at many of these global corps, and I have given up any hope of that happening. At least in the old days "long term" actually held some sway, but it doesn't anymore. SHORT term profit to look good usually seems to be the driving force for decision making. Bonus plans set up based on it are dangerous because it just reinforces that type of thinking. Beware how you incent your workforce.
The only good change I've seen is the recognition of how positive public opinion does impact profits which has let to considerably more charity work and some better public policy. In the old days it used to take someone that actually cared about society, now the bean counters pretend to also.