If you breach fiduciary duty the best thing you can hope for is to be fired. Executives have been criminally charged for it as well though. And while it has to be an intentional act of malfeasance, that gets pretty blurry when the shareholders hire thousand dollar an hour lawyers to come after you.

So while yes, the root cause is greed, the system itself is setup to feed that.

It's more complicated than just one law that says "you must be a bastard" I admit, but fiduciary responsibility is a core requirement of any publicly traded company and very much is legally enforceable (this parenthetical aside stands in for about three pages of niche caveats and overly wordy exceptions that I'm just going to shamelessly handwave away). At best a CEO might be found to be civilly liable, but ~~peasants~~ non-C-suite employees are criminally charged for neglecting their fiduciary duty every day in the US.