In the U.S., there is no fiduciary duty to minimize tax liability or to maximize profits. In any case the bar for a successful shareholder suit is extremely high, and executives are given tremendous leeway in situations where conflicts of interest aren't involved. I can't imagine that you could successfully sue a CEO for a company's not taking aggressive tax positions.
Achieving low tax rates is largely about keeping up with Wall Street analyst expectations. CEO's of public companies having to face a bunch of analysts every quarter to discuss quarterly earnings, including after-tax earnings, is a huge driver of this sort of behavior. CEO's are judged on how analysts view their stock, and it's a horse race. If some other company makes $0.05 more than you per share because of a lower tax rate, they are going to get credit for that.
Achieving low tax rates is largely about keeping up with Wall Street analyst expectations. CEO's of public companies having to face a bunch of analysts every quarter to discuss quarterly earnings, including after-tax earnings, is a huge driver of this sort of behavior. CEO's are judged on how analysts view their stock, and it's a horse race. If some other company makes $0.05 more than you per share because of a lower tax rate, they are going to get credit for that.