Zig is a small and simple language. It doesn't need a complicated compiler.
Rust is a large and robust language meant for serious systems programming. The scope of problems Rust addresses is large, and Rust seeks to be deployed to very large scale software problems.
These two are not the same and do not merit an apples to apples comparison.
edit: I made some changes to my phrasing. I described Zig as a "toy" language, which wasn't the right wording.
These languages are at different stages of maturity, have different levels of complexity, and have different customers. They shouldn't be measured against each other so superficially.