Let's leave the politics aside for a moment, but is there any benefit to even be on the "bleeding edge of software engineering"? I would assume these engineers are measured by reliability of their product instead of a techstack that looks good on a resumee?
The bleeding edge of your discipline is use of these I-beams, they enable you to build a comparatively elegant bridge which is far stronger and yet is less easily damaged by the elements than the iron bridges.
A "traditional" bridge engineer can point to examples of their preferred materials which have lasted fifty, a hundred years, and say look - we know cast iron works. You don't have that, and so there may be people who say "I don't want your new steel bridge", but on the other hand, clients may be swayed by the affordable yet better looking and more capable product.
In fifty years it's no contest, your steel bridges make sense, iron bridges made by your competitors are seen as old-fashioned and unnecessarily conservative. "Didn't they have steel?" "They didn't trust it". "Huh".
Now, of course it's not always so clear whether whatever you consider "Bleeding edge" is use of steel beams in bridges, or use of flammable aluminium cassette "weather cladding" on high rise buildings (a choice now seen as unacceptably dangerous). But just because it's how things were done by your grandfather doesn't mean it's a good choice today.
In your example your bridge builder presumably has a mature and stable software build equivalent of a steel ibeam bridge design that is basically going to be the same going forward. That’s more like when people still use cobol for decades because it works than when people are testing out the bleeding edge of software.
Whether Rust is mandatory to create defense Tech, that decision might have been influenced by many factors that apply also to any other start-up (time to market, access to talent, maturity of the ecosystem, skill distribution in founding team, etc)
You go look at older companies shipping product.zip.3 files around from someone's desktop and then it all comes in to focus.