Since defence is an area with a lot of secrets, for obvious reasons, inflation is a little greater. Not many information items or best practices are exchanged. It's not like other areas, where you can easily buy the competitors' products, disassemble them and see the improvements that can be made to our own assembly processes, as a result of what we discover.
That's one of the reasons for the inflation in defence matters. It's difficult to adopt best practices from others, or at least to adopt them as easily as can be done in other manufacturing sectors.
Armaments are an important factor, of course. The other factor is construction materials. These materials are often very specialized and they cannot be easily reused for other purposes.