This may be difficult to pin-down, but, nonetheless, I'm curious.
This is one claim within the field of 'economics', by and large, that I just don't get? Like... as far as I can tell- based on my occasional, independent 'research' on the topic- this.. is kind of a "myth" that, after a while, just 'took on a life of its own', so it operates almost as a sort of "business-world truism"? Especially since, from what I can tell, there are, in fact, *quite a few companies* here in the US that *don't*, oftentimes, make "value for shareholders" their number-1 priority, esp. firms like Costco (or Aldi and/or Trader Joes, to name a few) which, over the years, have, I think, been run on a more "stakeholder capitalism" type of model? And you almost-never hear about those firms getting prosecuted by the gov't, at least for *that* reason alone ("not prioritizing shareholders")
Like... *are* there any major, oft-enforced laws (esp. at the state level) and/or recent court rulings- again, in the US (if not similar nations)- that do, in fact, "require" the executives running publicly-traded corporations to, as their 'main/foremost duty' under the law to "generate value for shareholders"? *Can* a shareholder who, say, owns stock in Walmart, in theory, "sue" the firm if they "have hard evidence" that its executives and managers, "didn't try to maximize return for shareholders"?
Ah! The truism favourite of certain elements of all business schools.
The rumour (it does certainly feel like a truism nowadays though) would likely originate in Dodge v. Ford Motor Company, 204 Mich. 459, 170 N.W. 668 (Mich. 1919) aka "John F. Dodge and Horace E. Dodge v. Ford Motor Company et al".
https://h2o.law.harvard.edu/cases/3965
This conflict erupted between Henry Ford and two brothers Dodge, because Ford did no want to share the company profits quite as thoroughly as could have been possible because he thought they they were using their minority stake to milk his company for funds to create their own competitor. Ford had been cutting the price of the Model T and raising workers wages significantly during the model's run. Ford wanted to use the capital accumulated to invest further in plants and workers to make even more cars instead of more special dividends. We could say as a long term strategic goal. At least publicly. The Dodge brothers of course wanted money now, arguing Ford was undermining the value of the company because the investments were not needed at the time basically. And trying to squeeze them out of the company (which wasn't completely taken out of the blue either). Considering the men started their own rivalling car company later it's not like Ford was wrong in his suspicions either.
In the short term the Dodge brothers won the case and the court forbade Ford from doing what he planned. Longer term however the case did reinforce the business judgement rule, i.e. that the managers of the business have a lot of leeway to determine in the short and long term what is (in their perception) best for the business. Effectively meaning you can do things that aren't solely immediately beneficial to the stockholders and that other stakeholders' needs are relevant. So other cases go the way of the business managers over the 1950s and 60s.
So basically that's the origin of the idea, conceptually and it's often considered so. But bear in mind many other cases ruled effectively in opposition to the Doge/Ford case, so what gives?
The answer is likely economist Milton Friedman and what has become known as the Friedman doctrine. This implies that the social responsibility of corporations is to increase it's profits, basically the title of a 1970 essay he wrote for the New York Times. In Friedman's view, corporations considering anything other than profit leads to totalitarianism (Capitalism and Freedom [1962]).
This a time when the American economy is stagnating and the business world is looking for new ideas of how to do things differently. Other economists and businessleaders would join this "cause" influencing amongst other things, business schools who would teach this to it's graduates. And it has impacted the business world of the 1980s and 1990s and on, not insignificantly because (in my opinion) because the collapse of communism as a system in the 90s more or less proved it so to say.
Now, this way of thinking (the "Friedman doctrine") has been challenged of course, e.g. Naomi Klein in her 2007 book "The Shock Doctrine". But I'm a little out of my depth and a lot of this is going to run into modern politics so I prefer to veer out of the way of that iceberg.
Also note that it isn't so much that the government rules this or that in these cases. There is no law that says that business must maximize profit or shareholder value. These are private court cases, where judges have to decide which point of view is given primacy weigh the various merits of the cases. If a privately owned company isn't run to profit or value but none of the shareholders complain the government won't interfere (nor does it even in court cases, the judicial system merely provides the adjudication.
In short there are some prominent court cases delineating what the responsibilities of business and their managers should be, that probably the ur-origin of the idea. But these are also something that is constantly being reshaped by economist (and their theories) and business leaders. Without a really quantifiable correct answer competing theories exist on how to best run businesses, and these are also subject to trends with sometimes a successful model gains quite a lot of primacy.