The simple answer is politics. It's political considerations. When political parties decide there is political benefit in politicizing a defence issue because of the large money attached to it—and I understand that incentive—you suddenly get into this problem. We saw it before, going back to the nineties—that lengthy project to replace the Sea King helicopters with the EH101, and the cancellation. The simple answer is political involvement.
It's also reflected, of course, internally, in the context of the professionalization of the bureaucracy. Yes, they are highly professional, but they also play the game of the second guess: What does the government want? If the department feels the F-35, in the process leading up to the election of 2015 and afterwards.... If the government is not likely to look favourably on moving forward quickly, the department won't move forward. They will find other things to push forward. It's the dynamic between government on the one hand, and the perceptions and beliefs in departments on the other hand. When combined, these explain how these things drag on.