Of course they didn't have a choice. It was the board, not management, and they had a fiduciary obligation to sue. They'd have been sued had they not, and they morally have an obligation to represent shareholders so they'd be awful people if they didn't.
Nobody suggested they did. They have an obligation to act in shareholder's best interest. In this case, they'd have a very difficult time explaining that not suing would be in shareholder's best interest.
