The owners of firms are in business to make a profit. As the great man said, "It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest."
The salaries and wages owners pay their employees are expenses and the owners have no incentive to pay their employees more than the employees add to the value of the firm. Suppose I am the owner/manager of a brewery. A potential employee may come to the table with little or no skills, but would contribute $10.00/hour to the value of the firm. I would pay up to $10/hour (including fringes, employer FICA, etc.) to hire him/her. Other potential employees may show up with more in the way of training and skills and would add more to the value of the firm. I would pay up to the marginal value product of those workers to hire them. As the owner and manager, I can monitor my employees and determine their contributions to the business. If my employees find their skills and training are worth more in another business, they should change employers. In doing so, they improve their own incomes and the efficiency of the marketplace. They end up where their talents add the most value.
Suppose my beer is prized by my customers and I become wealthy in the process. I now want to enjoy the fruits of my labors and want to turn over management of my business. In interviewing potential managers, one candidate whose training (in agricultural economics

),experience, and vision make him/her my clear choice. I estimate the candidate could increase the value of the firm by $4,000,000/year. What should I offer him/her? I face the principal-agent problem. I, the owner (principal) have to be concerned that the manager (agent) will act in my interest to maximize the value of the firm, rather than padding his/her own nest. I might offer the manager profit-sharing, partial ownership or other incentives to overcome the problem. I would be willing to pay the manager up to his marginal product. If I can hire him/her for less, I further pad my nest.
If executives aren't acting in the best interests of their shareholders by increasing the value of their firms, they face dismissal by their corporate boards, their corporations may be taken over by other corporations, or by private-equity firms.
They are responding to the tax code -- it's not a problem of their own creation, IMO.
I don't question the presence of "cronyism" and rent-seeking. Shareholders should demand and receive better corporate governance. Rent-seeking is a whole other topic.
Funny you should ask. Greg Mankiw addresses the issue is his blog today (
http://gregmankiw.blogspot.com/2013/12/on-measuring-changes-in-income.html) and the Journal of Economic Perspectives article he links.
Steve