I have had, mostly technical, roles in some projects that could be classified as you did. Although I don't claim to have any authority in managing projects at t

I have had, mostly technical, roles in some projects that could be classified as you did. Although I don't claim to have any authority in managing projects at this scale, my best guess is egoism. All these large projects have people involved and those people all work according to their own agenda. Including the people involved at the client side. Spending someone else's money tilts any decision towards personal gain somewhat, consciously or subconsciously.