So far no one has managed to produce a programming language with dependent types that compiles to efficient machine code with zero overhead like Rust and C do, so the reason to not have dependent types in Rust is to be able to produce efficient code (which Haskell doesn't even without dependent types).

Obviously if such a language is possible to make and gets made, it will be the strict best programming language overall and make all other languages obsolete (just like Rust obsoleted C/C++, etc.)