The simple answer is that no one has ever put together a solid enough proposal that ended up getting accepted. As far as I'm aware overloading has never been explicitly ruled out by the lang team.
Overloading is known for causing issues with type inference and human-readability. (It's not an accident it's called "ad-hoc polymorphism" by type theorists.) In Rust, everything that overloading is useful for can be done by means of traits and generics in a much more regular, easier-to-reason-about manner.
I won't speak as to readability, but at least with regard to inference allowing one function definition for any given number of arguments wouldn't cause an issue. I know it's something I've wanted in a few niche cases. Not full-on overloading, but still quite useful.