I don't think that is the reason. When Raytheon or other contractors perform software work under a DOD contract (i.e., they charge the labor to a contract) the government generally gets certain exclusive rights to the software created. Raytheon is technically still the copyright holder, but effectively is required to grant the US government an irrevocable license to do whatever they want with the source in support of government missions if the code is delivered to the government. Depending on the contract, such code may also fall under blanket non-disclosure agreements. I believe both of these are incompatible with the GPL, and the latter with having a public fork at all.

The company could work this out with the government, but it would be an expensive and time-consuming process because government program offices are slow, bureaucratic, and hate dealing with small exceptions on large contracts. They might even still refuse to make the contract mods required at the end simply because they don't understand it or they are too risk averse. Legal is likely of the opinion that it isn't worth trying, and the Raytheon program office likely won't push them unless they can show a significant benefit for the company.