It allows Boeing, for instance, to patent their version of hypersonic propulsion (again, a conjecture, not a real example) without worrying about the informatio

It allows Boeing, for instance, to patent their version of hypersonic propulsion (again, a conjecture, not a real example) without worrying about the information becoming public knowledge; which a non-protected patent would require. Government or agency patents are a matter of course and provide attribution and protection to their authors (similar to public patents). There are plenty of technologies the US govt researched and implemented that they did not patent and instead released directly to the public domain. Many of those related to Arpanet and baseband cellular technologies are key examples. So your point is moot. They do both, it's discretionary to their strategic interests, in much the same way commercial entities will sometimes patent their research but make it freely licenseable.