USDS and 18F are staffed by confident people from industry. The federal government, when it comes to software, is not as incompetent as you think.
Instead of having a department make software, they are supported from a vastly superior group of developers that work temporarily with that department.
Maybe its too much to ask, but shouldnt the company providing the software also employ the talent that is used to make the software?
Having some experience with why government lacks organizational development competence (TLDR; short-sighted management with the wrong goals), I don't think they can do that—they literally are addressing the wrong problem—but the idea wasn't to be a silo of technical skill.