Because they don't grow large or need a multi-person team. CLI tools tend to be one & done. In other words, it's saying "Zig, like C, doesn't scale well. Use something else for larger, longer lived codebases."
This really comes across in the article's push that Zig treats you like an adult while Rust is a babysitter. This is not unlike the sentiment for Java back in the day. But the reality is that most codebases don't need to be clever and they do need a babysitter.