You see, these contractors tend to hire retired admirals and generals directly out of acquisitions positions and onto their boards. The contracts are written in ways that make it hard to punish shoddy work in a way that doesn't make the government side look bad too, so they tend to let slide what is kept out of sight. After all, if someone makes enough noise, then your contract may end up on the news or even worse, on the hill. If that happens, contracts get yanked, people get reassigned or lose their chance at a kushy spot on a board in a few years. It varies by contract and organizations, some are much better run than others and tend to deliver good quality.

It's so much money that all the best scammers can't resist, and so much bureaucracy/regulation that all the honest folks reach their limit and move on.

Any single issue can be addressed, but this is a meta issue.

There’s overhead to a more detailed specification. Creating it takes time and people need to read and understand it, then you need someone to inspect the results to keep someone honest. It remove flexibility, and even tiny changes require large updates to the specification when then need to be reviewed etc.

So simply adding details to a specification inherently reduces efficiency.