Why do mega-Projects fail so often?

Lack of planning , budgeting, time management and work distribution and if there no vision then nothing is at place. Some good example of successful Mega projects are Burj Khaleefa so we can take some cue from it .

In my opinion there are three main common features (not limited at these), one of the main reasons of high failure of mega-projects is flawed strategic decision making. Other would be high level of uncertainty (which characterizes mega-projects), the methods used by companies are only approximate procedures. Third of the main reasons of failure was illusion of control.

I see that the main reasons for mega projects are:

Confusion of accountability

Ineffective & iefficent communications methods with larger groups

Weakness of most project management tools to manage mega projects effectively, and when such features are available, they are complicated to a great degree.