Yea, so mainly one situation that isn't explained here. Is that the moment you introduce a different language besides C, you now need to talk between C and this other language. This is called language bindings.
The problem with this, is the moment something is changing in C, and this method or interface is used by some Rust code, the Rust binding to C or C to Rust binding is failing, cause all kinds of issues.
Long story short, is that by introducing this additional language you created this technical issue of language bindings. And people who just want to work with C code, now suddenly also need to think about Rust bindings, while they previously didn't need to think about that. As if the Linux kernel isn't complicated enough, introducing this language binding issue is cause more (unwanted) work for some people.
In the end the "C" people are blaming Rust if something fails. And the "Rust" people are trying to explain and help the "C" people to introduce those bindings. waaaahhhh