Rust has hidden allocation, no planned static stack analysis or limits on recursion, little to no control over how allocation happens, no ability to guarantee a panic won't happen and thus no ability for the programmer to guarantee eg. essential external resources are cleaned up.

The guarantees that zig seeks to enable (this being the key phrase, it does not guarantee them just by its use, nor has the project solved all the problems this entails) the programmer to provide are non-goals of rust.

Ie. the projects have completely different goals. The things zig want to provide would make rust unusable if it tried to provide them and vice versa.