cynically speaking, its probably that contracters deliberately delay delivering projects as long as they can to ensure maximum cash (great when you're paid by the man-hour). Fines and penalties were then introduced to try and dissuade this. Contracters thought bugger this, it means we have to work hard, and so lots of bigwigs and paper-pushers take tours to see how hard the project is to complete in the allotted timeframe, and so these desk-jockeys say oh we don't need it to do this or protect that, we can lop it off.
Net result - contracters can slack off and still get overpaid and then deliver what they're told to, which happens to be a completely gutted version of the original project.
In reality, theres a lot more to consider, things like rising costs, inflation, unexpected demand for different resources or supplies, the inevitable human error which needs to be corrected, machines breaking down.. and much much more
