I said it's their biggest priority, not their only priority... solving a problem that doesn't cost money and the solution doesn't make money is bottom of the barrel. Come on guys, be real.
Is there an incentive to do that? Yes, or at least it's obviously quite possible. But is there an obligation? No.
Relative to the comment you were responding to, it sounded like you were defending the idea that an obligation exists.
The distinction matters because if such an obligation did exist it would effectively excuse a lot of bad behavior.
If you look at the case law for fiduciary responsibility, then you'll find that executives have a strong obligation against self-dealing (decisions that clearly benefit them at the expense of the shareholder), but not much else. The "business judgment rule" makes it generally lawful for executives to make decisions that you, the shareholders, the judge, or anyone else might consider to be bad business judgment. It couldn't really be otherwise, since the difference between wasteful spending and a wise investment in the company's reputation might be unclear even decades later.
If shareholders disagree with an executive's business judgment, then their remedy is to fire that executive. That remedy has nothing specific to "making money"--the shareholders are just as free to fire a CEO for excessive attention to profit as insufficient.
You linked an article about fiduciary responsibility, and that's also a legal obligation. If I'm an executive and I route contracts to a vendor that I own for personal gain, then the shareholders can sue me and I will lose. The state will likewise enforce that judgment, if necessary with physical force.
If I'm an executive and I choose to spend too much money (in someone's opinion) auditing a git hosting site for malware, then the possibility that I'll get sued for that and lose is zero. That's the "business judgment rule", which is a legal term of art that you can search. The shareholders might fire me, but only in the same way they could fire me for anything.
The financial incentives are obviously as you say, but the difference between "things I do because the state will physically punish me if I don't" and "things I do because I want a high-paying job" is valuable to me. I could probably make more money than I do now if I worked for a payday lender or an online casino, but I don't think that obligates me to do so.