From Loren Thompson writing at Forbes, who gives his take on the top five reasons weapons systems are cancelled.
1. Changing threats: the USSR does not equal Al Qaeda does not equal China.
2. Excessive requirements: SBIRS is used as the example. NPOESS would be an even better example.
3. Cost growth, often as a result of low-balling the initial estimates or counting on immature technologies. Self-explanatory.
4. Missing constituencies: there is of course the issue of office holders. Thompson doesn’t mention it, but the importance of staffer support is also essential. There are many who can mortally damage a program and none that can make it happen, which is a collaborative effort.
5. Bad management: the military tend to be inexperienced and the civilians tend to be other than A-team members. Plus, the military tends to avoid using the engineering and scientific skills its members possess, and as such, those skills atrophy.
Using Thompson’s list, my informal take (in order) would be 2, 3, 4, 1, and 5.
I’m sure the Defense Acquisition University has a case study on this somewhere.