Not for lack of trying. The Pentagon does try to account for the money, and in fact they can with enough looking. But it’s the most complex accounting system in the world, plagued with legacy systems that don’t talk to other legacy systems, doesn’t have a way to move those systems to newer systems, and so on.

A bunch of companies have tried to come in and build new accounting systems for the Pentagon, every single one of them has either dropped the bid after looking at the problem, or been unable to fix it.

It’s probably an unfixable problem.