Cynical answer?
MBAs teach how to figure out which businesses are valuable, get in charge of them and get rich from taht, not how to make the business in question perform well.
The MBAs that you are complaining about, as well as George W. Bush, illustrate their effectiveness at what they were trained to do. That you don't see how effective they are merely indicates that you are looking in the wrong place.
Cheers,
Ben