My tuppence's worth
I've always considered that most procurement problems arise from the high rate of staff churn, post swapping and departures. The chances of a team coming together, staying intact for a whole project's lifetime and then going on to do the next one together is zero. The chances of there being anyone in the team who was there at the beginning of a project is pretty low too. I reckoned that the average in-post time was less then 2 years. Maybe it's a bit better in the supplier base, but in the PE it was pretty bad, not helped by the military's pathological hatred of leaving anyone in post for more than 3 years and the civil service's outdated views on staff skills, post mobility ("any grade 7 is qualified to do any grade 7 job anywhere in government"), etc. Too easy to transfer out of a doomed project.
In an environment like that a lot of mistakes are going to be made, and no one is going to be left there to learn from them. Consequently it's like everything that gets done is being done by people who are almost by definition amateurs in any one particular domain of military capability.
I remember one guy bemoaning the number of different types generators they had. Right answer would be been 1. The actual answer wasn't 1, not even close.
It's not helped by the slow pace of procurement and politics making a mess of things. Guess what - build a lot of stuff quickly and keep doing it and there's a good chance it'll get better.