While the revolving door is always a potential issue, and I'm sure it happens, I don't think that's a key problem for the DoD. When government officials leave office they're required to
not do work, for a period of time, on things they controlled, and the penalties can be steep. That reduces incentives for the worst of abuses. Also: a US government employee who retires after 20+ years has a guaranteed pension; it's nice to get more on top, but not by risking it.
No, I think the pressure primarily comes from the DoD procurement process itself. First, you have to develop the requirements. The Air Force wants a plane, the Navy wants a plane, the Army wants a plane. If you say "yes" to one & "no" the others you get a political battle. A bright person says, "I know, we'll make a plane for everyone, and the volume purchase will make it cheaper!" "Great!" everyone says. They each bring in their laundry lists of what they want the plane to do... if you say "no", then they probably won't fund it, so you have this HUGE list of requirements. Now the plane (or whatever) has to do everything.
Then it goes out for bid. Only the lowest bid will win, so contractors will do their best to make it a low price for a massive number of requirements. They're under great pressure to underbid the real costs, and when you do new things it's usually more expensive than you imagine. Yet those costs will still look eye-wateringly big (because it's trying to do everything). Contractors will then say "don't require that 'bunch of useless technical data and those technical data rights... it'll be cheaper!". In addition, every time you learn something, you'll need to make a change, and that will result in a change request with a remarkably high price tag. That's partly because the contractors are motivated by profit, but to be fair, they were often pressured into unrealistically low starting costs by the process.
Many of the DoD's problems aren't from "evil government officials" or "evil contractors". Many really are trying to do good things. Sometimes the problem is that the DoD procurement process has some perverse incentives that sometimes results in very strange outcomes.