> The board of a company must act in the interests of shareholders

I think you don't understand what this phrase means. In a publicly-traded company, "the interest of the shareholders" does not mean "whatever the shareholders want"; it means "whatever is best for the company." That means money.

It may be possible to be both profitable and moral; but if it isn't, the fiduciary duty obligates corporate officers to choose the profitable path rather than the moral one.

The easy way of looking at this is that there beyond complying with the law, there is no general obligation for companies to behave morally, but there is a general obligation to behave profitably. So it's not hard to see why they make they choices they do.

> It's entirely possible to still satisfy those requirements by building a sustainable and moral company.

It is, but it's a lot easier to be not sustainable and not moral.