Except that there are limits on fiduciary duty. It should not be confused for a right to earn money. Losing money on a bad investment is part of the game. The duty that they have is to carry out the terms of the investment prospectus and nothing more.
Shareholders have the right to not get lied to by executives. The SEC forces companies to put lots of stuff into their annual reports, giving companies lots of opportunities to lie to shareholders. Companies basically write "we aren't doing anything morally ambiguous" in their annual reports, almost always lying when they do so.
Except that intentionally making bad investments fully knowing that they are bad investments is not something you can put aside as just “bad investments you lost money on”. This is absolutely something the board needs to hold the executive team accountable for and is part of their fiduciary duty.
I bet the chairman, Mark Zuckerberg, is going to steer the board to get right on with punishing the CEO, Mark Zuckerberg, for his careless administration of the company.