Whether it's a legal requirement or not, companies definitely act as if it is. Setting a company on fire to acquire short-term profits with a golden parachute guarantee is the pattern for executives of public companies under American capitalism.
Oh let me be perfectly clear here, I know that that is how things often shake out, especially in the US. What I am talking about is the way people defend businesses that behave this way.
They act as if they have no choice, that there is some legal mandate to just wring out a company all day every day and damn all consideration beyond “I can make another dollar this second.”
There has been this odd trend over the last few years of mischaracterizing what this means/what that duty translates to. People talk about it as if every CEO has to redline the company at all times and never think about longterm consequences for literally any reason. Every single cent that can be extracted right now must be extracted or the investors will rise up in all their anger crying out "FIDUCIARY DUTY!" as they drag the poor CEO off kicking and screaming.
Companies can think longterm. They're allowed to sacrifice short term profits for sustainability/longevity. I don't get where people get this idea that they can't. To me, "fiduciary duty" has become almost memetic - it's some weird hand wave-y line people throw out to excuse businesses being short-sighted, as if they never had a choice.