You missed a major cause of public sector project failure
The elected twit(s) "in charge".
Based on their expertise dervived from winning a popularity contest, in which the majority of the eligible voters couldn't be arsed to vote, they feel they are qualified to tell international academic experts, and people who have spent their entire proffesional lives working in the relevant field, that they do not know what they are talking about, if they dare to comment on a project/proposed project. (e.g. Charles Clarke and the LSE report on ID Cards)
They also tend to do the classic of pick a politically acceptable price and timeframe, with either no clear scope, or a politically mandated scope, and then go tell the PM to deliver, not having done any of the sensible pre-project research, feasibility and prep work.
This isn't just in IT either, look at any defence project.