This is not unique to Rust. The Python async runtimes are not compatible with each other as well, there is AnyIO which is a wrapper that acts as an abstraction

This is not unique to Rust. The Python async runtimes are not compatible with each other as well, there is AnyIO which is a wrapper that acts as an abstraction that makes things easier but it's still not as implicit as with languages with builtin runtimes. There is also an ongoing effort to make Rust async runtimes pluggable.