You're not wrong about defense however there is a huge caveat. From what I'm told, when a company in defense (in the US) uses FOSS they must sign a waiver saying that they will be responsible for all updates and vulnerabilities discovered with said library. This also means that if the library stops being maintained, the company is responsible for maintaining the library.
I know that the reason why RHEL is preferred over Ubuntu or other distros is the fact RHEL has a paid license and provides regular updates to even "dead" or EoL libraries and packages.
Having said that, I wish more companies would take that dive. I've been in situations where the company would not sign a waiver so we had to essentially re-create a functionality that a FOSS library already provides.
My parents and I were just talking about this.
We're all in agreement that the moment that diamond goes back to India (or any country in SEA), it will "disappear" and never seen again.
I really like rustlings.