It's not. But that the system we're currently under. In a better world, you'd have employees, local government, consumers as well as obligation owners on the companies boards.

Because of incentive alignment. They are the only ones incentivized not to do something stupid with their own resources.

Because they created the production; it they couldn't control it then they'd have no incentive to create it and there'd be no non-state-owned businesses, exactly as happened when China was fully communist and still happens in North Korea today. Capital doesn't grow out of thin air just from "working"; the only people who think it does are those who've never tried to build a successful business.