Maximizing shareholder value is a management philosophy that became increasingly prevalent between 1975 and 2000. In both management ("What we should value and pursue") and case law ("What you will be sued and found guilty for not doing").
Why did it become popular? Because there were a huge number of inefficient companies at the time that were continuing business as usual under some guise of "We think this is best." While Japanese companies ate their lunches by working harder, faster, better, and smarter.
Holding management to shareholder value -- and sueing the heck out of them when they didn't focus on it -- was a more objective measurement of effectiveness.
After 2000, it became clear that the metric had become the target, and was now being pursued with a myopicness that was to the detriment of the company.
There are few absolutes in "high performance"
But nobody said they need to break the law, or hurt employees. Given the constraints of the law, they have a single mission of maximizing the share price. Which is exactly what Microsoft and other companies do every day. If the environment gets in the way of your business (i.e if you are an oil company) then you will only care about the environment to the extent that you are legally obligated to.
There are dissenting papers [2] mostly revolving upon Dodge v. Ford Motor Company, but there are many intractable problems when you assert such primacy. Over what duration? As compared to which company? Accounting for intangibles? Valuation of non-monetary factors? Accounting for market gyrations? Primacy by what percentage? That dissenting paper glosses over much of the nuance of Stout's thesis [3], as well as case law ever since that point to the problematic practicalities of courts deciding how companies should carry out the distribution of the benefits of organizing stakeholders together.
So many people who should know better keep repeating this canard. Shareholders can certainly mount a challenge through corporate governance channels for example, but they fare poorly when mounting a challenge through the courts.
[1] https://corpgov.law.harvard.edu/2012/06/26/the-shareholder-v...
[2] https://clsbluesky.law.columbia.edu/2022/04/26/why-we-should...
[3] https://scholarship.law.cornell.edu/cgi/viewcontent.cgi?arti...
Why does it matter? Well, because the higher valued your company is, the more investment you can get, and with more investment, the better you can beat the competition.
And if you don't do it (bad stuff), then your competition will do it and will ultimately will beat you.
So it is basically the only way to survive. That is, keep growing. Stop growing, and you are on path to demise. No public company have the luxury of saying "Well, we have grown enough. Let us just focus on sustaining what we have got".
Google for something like "obligation to maximize shareholder value" if you want to find numerous articles debunking the myth. Here's a good one [1].
[1] https://www.nytimes.com/roomfordebate/2015/04/16/what-are-co...