In the UK, company directors have also vastly outpaced everyone else in earnings growth since the '80s.
Their compensation is decided by a remuneration committee. The remuneration committees are composed of company directors from other companies to give them "independence", shareholders play no part in the process. It's a you scratch my back and I'll scratch yours thing.
Why don't the shareholders object? Because the shareholders are mostly funds who similarly have directors.
They also compare the remuneration with the one provided by peers. Of course every CEO is above average and deserves to be paid better than the industry average. Unsurprisingly, the average compensation increases year after year...