People who write C code ignoring warnings are the same people who in Rust will resort to writing unsafe with raw pointers as soon as they hit the first borrow check error. If you can't force them to care about C warnings, how are you going to force them to care about Rust safety?
I've seen this happen; it's not seen at large because the vast majority of people writing Rust code in public do it because they want to, not because they're forced.