[namdnay]

The reality is much more mundane.

If they don’t implement that poorly worded requirement, they are entering a world of pain of having to justify the deviation through 10 layers of project managers and qa, all from different organisations (either customer or other contractors). And at the end they’ll be the troublemakers who delayed the milestone

So why bother?

[Eddy_Viscosity2]

This is also true I don't doubt, but I've heard directly from contractors that they look for requirement holes so they can monetize them to the maximum extent possible.

Having a dedicated developer team who work directly for government whose sole job it is to make and maintain software like this for the long term, still seems like the most cost-effective and durable solution.