I doubt that increase in CEO pay has much to do with objective value because it would be so hard to measure.
I suspect it would be a mixture of (a) companies being bigger and able to pay more as others have said, (b) mutual backscratching amongst the boardroom set, as other have said, © “cat food purchase strategy”, and (d) increased churn and the “heads or tails” game.
Cat Food Purchase Strategy
By cat food purchase strategy I refer to an experiment I once heard of (so it must be true, right?) where a cat food company raised its prices above its competitors without changing anything at all else about its marketing or product in any other way. Their sales went up not down. Presumably, above a certain base level, people can’t tell whether cat food is better or worse for their cat, or liked or disliked by their cat, so they just assume the more expensive one is better.
What will cause a company to do better or worse is a “dark art”. It results from a mixture of luck and skill, and the skill comes not just from the CEO but usually an enormous team. So it’s very hard to objectively judge CEO’s on performance, so people assume that the CEO’s who demand the highest pay are the best. Which creates an upward spiral as CEO’s keep demanding more.
The “Heads and Tails” Game.
I don’t know if you’ve ever played the game where a roomful of people stand up, and each chooses “heads” or “tails” by putting their hands on their head or their ass. Someone tosses a coin, and those that chose wrong sit down. Then those left standing choose again, and so it goes till there is one person standing left. This person has then chosen correctly on a coin toss often for more than six or seven tosses in a row. What a genius! Except of course they have exercised no skill. It’s just that out of a roomful of people, someone is bound to luck out.
Fifty years ago, people stayed with a company and worked their way up. Now people change more often, and professional managers buzz around between large corporations. There are tens of thousands of them at least to begin with. Some of them are bound to luck out in terms of always being associated with extraordinary success. So you end up with a handful who can be perceived to have The Golden Touch, who can write their own ticket.