Genuine question because I think I might be wrong on this one, or maybe misunderstanding what you're saying - aren't there cases of shareholders suing CEOs for not acting in shareholders interest and winning? If there was no legal obligation to act on behalf of shareholders how could they win those cases?

My understanding is those kind of cases aren't common because a) they are hard to prove, b) the people being sued if they actually have the money to make it worth suing them also have the money to fight it, and c) it's a really bad look for an investor to be suing a previous member of their portfolio and would a strong adverse affect on their deal flow

Unless you're saying there is no explicit legal obligation / fiduciary duty in law, but it does emerge from civil court cases, which is how I understand it, but short paragraphs are not a good place for the amount of nuance so I just said "legal obligation" as a shorthand for something real but very complex.