Because money is a finite resource, is only useful when it moves, and when only a few people hold the majority of the purse strings, they gain an inordinate say in what problems get enough funding thrown at them to be solved either through active favoritism or passive inaction?
Please, we all know someone is going to make the argument you just did. It is the lowest effort, most intellectually shallow argument you can start with. In fact, it's a thinly veiled ad hominem if you think it through long enough as it boils down to "Poor people are poor because they suck."
In the United States, we hold it to be self-evident that all men are created equal. Period. When inequality of some form becomes so ingrained in our society so as to become everyday and even praised, it is only natural for a culture that holds equality amongst people as a core characteristic to wonder if something may be a bit off about the system.
To answer your question...
Why should someone who acts as an executive be worth so much more than the carpenter or operator in the eyes of their fellow men? Businesses are social structures, nominally intended to benefit society (often redefined as shareholders for the hard core capitalists out there) as a whole.
Yet... We see that executives and C levels get an exaggerated share of the value produced by the structure.
"But they have business savvy!" I imagine someone would retort.
Doesn't justify the compensation disparity. They just got an MBA and learned about how to structure a business while the carpenter was learning to woodwork. A business for business sake without professionals capable of understanding and executing the craft or service at hand is meaningless.
"No one would accept the responsibility without that level of compensation! It's too straining!" Another may retort.
That sounds a bit disingenuous to me. Is it mentally straining? Of course. Not so much so that orders of magnitude difference should justifiably exist between the average worker and the top of the pyramid.
Nominally, everyone should have an equal chance to start a successful business. Realistically, the later you come to the game, the more the cards are stacked against you, and in favor of everyone who is already there.
I would like to see society move in a direction where there wasn't so much incentive to "get money at all costs", but rather to solve pressing issues that are having a clear and present deleterious effect on society. The inability of many mundane laborers to be able to keep up with the market is one sych issue.