But I think what matters in this particular context is that Rust does not support function overloading and this restriction also applies to functions implementing operators. I think this may be why the parent comment claims that it is not really overloading. The meaning of "overloading" is a bit ambiguous here.

So for a concrete type vec3 you cannot define both <vec3> * <double> and <vec3> * <vec3>, which makes type inference a lot easier. It also makes Rust operator overloading less expressive.