I assume it's because they view private industry as a US asset, and don't want Russia or China hacking them (to steal IP, or gather information, etc.).

Promoting cyber security in the civilian workforce is also part of the DoD's 2023 "Cyber Strategy".

The Department will take action to foster a culture of cybersecurity and cyber awareness. We will establish an expectation that senior military and civilian leaders possess a baseline fluency in cybersecurity issues. The Department will develop, fund, and implement technical curricula across different levels of professional military and civilian education, emphasizing General Officer and Senior Executive Service leadership courses.

https://media.defense.gov/2023/Sep/12/2003299076/-1/-1/1/202...

They're also trying to promote cyber security in open source software: https://www.nsa.gov/Press-Room/Press-Releases-Statements/Pre...

That's not to say you're wrong about the NSA probably having backdoors in critical software like the Rust compiler.

Or... (puts on tin foil hat) added it themselves.

As a C++ programmer, I really want to find a spare week or two to learn Rust.