Why are most managers in corporate America woefully incompetent???

I have worked in corporate America for about ten years now. In that time, I have worked for 6 companies. In every company, but one, I have had managers that are completely incapable of managing people. The higher-ups ume that because someone is good in their job, they are also able to manage other employees. At first I thought it was just the particular company I worked for, but I have realized that it is widespread throughout most companies. What can be done about this?