The answer, dear Goldy, is simple and straight-forward.
More than an ordinary investor, a potential nominee to a board of numbskulls to a public corporation is required to do due diligence because once he accepts the position, he has public fiduciary responsibilities and liabilities. If he is ignorant and lazy, he has no excuse if something bad happens to the corporation, its assets, or its shareholders.
Under Sarbanes-Oxley, stupidity is no longer an acceptable defense. A deadhead among deadheads can still get sued, indicted, and be subject to many other sanctions. Business law applied. All IMHO.