If the CEO makes a million dollars a year in a company with 100,000 empoyees, wiping out that entire salary would add less than $0.01/hour to each of the employees' wages. Also, then you would not have a CEO, which you might actually need sometimes.
The shareholders can't just hire a random janitor at a janitor's salary to be the CEO and expect to not lose more money to unqualified decisionmaking than they would've had to pay a real CEO.
Likewise, they can't just make zero profits forever, because otherwise they couldn't raise capital. If they're a new company they need that investment in order to buy land and build the factory etc. If they're an existing company then they still need that, or the shareholders would sell their shares and the only buyer would be a corporate raider who wants to tear down the factory for scrap and sell the land to a condo developer.
Salaries and profits are relative to the market average. Unless the company is paying its executives more than the average company, or making more profits than the average company, they don't really have a surplus they can give to the workers without becoming uncompetitive.
Plenty of profitable businesses can afford to pay employees more. The fact that they are profitable is testament to it. They choose not to, because their employees don't have enough leverage in the employee-employer relationship. Unions change that.
The fact that not unionizing was how they got the work to begin with. If they tried to do the same thing there, the company wouldn't have any reason not to move back, which the workers in the new place obviously don't want.
As long as the company pays its owners more than their lowest-paid employees, it can afford to pay their employees more, without going out of business.
There's plenty of profitable firms that can't just pack up and move to Mexico.