They contributed code that they needed, that is not giving back. I am speaking about actual long-term maintenance and/or money, which isn't mentioned anywhere.

See, the problem with these code contributions is that they are just that: One time effort. In most cases, this code will be handed over to the core maintainers, who will then have to deal with it for the rest of the project's lifecycle. There are many documented instances in which FOSS projects are actually suffering because of contributions like this, as they are struggling to maintain the added features long term.

But all the people downvoting this care about is that a public money drain like the military writes some code and throws it into the faces of FOSS developers, even completely disregarding whether these improvements are actually relevant for the everyday user of the software. And again, by contributing I am referring to actually funding the project with significant amounts. We are speaking of a public entity that spends multiple millions on a single fighter jet.