Because Rust-style resource management is not only about performance, but also about correctness. And the ML crowd cares a lot about the latter - rightly so.
I'd kill for a language with ordinary ML types for values (integers, strings, etc.), and substructural types for objects (file handles, database connections, etc.).
I'd kill for a language with ordinary ML types for values (integers, strings, etc.), and substructural types for objects (file handles, database connections, etc.).