I would expect that the largest factor is cultural, and of course it's possible to inculcate safety culture in a team working on a C or C++ codebase, but it seems to me that we've shown it's actually easier to import the culture with a language which supports it.

Essentially Weak Sapir–Whorf but for programming languages rather than natural languages. Which is such a common idea that it's the subject of a Turing Award speech. Because the code you read and write in Rust usually has these desirable safety properties, that's how you tend to end up thinking about the problems expressed in that code. You could think this way in C, or C++ but the provided tooling and standard libraries don't support that way of using them so well.

The thing is. There always was a strong theoretical case that Rust should improve software quality (not just because of the fact that you have a lifetime system). The only reasonable counterpoint was that this is theory, and large scale experience is missing. Maybe in high quality code bases the mental overhead of using Rust would outweigh the theoretical guarantees, and the type of mistakes prevented are already caught by C/C++ tooling anyways?

The (in recent years) rapid adoption of Rust in industry clearly shows that this is not the case.