I don't think Rust users are relevant here. It primarily comes down to personal preferences, and since Zig and Rust are so different, some will be drawn to Rust and others to Zig. If you really like a language and it suits your needs, be it Rust or any other, there's no need to look to switch. I think that the audience Zig is aimed at is low-level programmers who haven't taken a liking to Rust, which is the majority of them. Rust isn't very popular among experienced low-level programmers (certainly for a language that old), and I guess Zig is hoping to be more to their liking.

For example, I find Rust to be far too similar to C++, and it shares most of the problems I have with C++ only with much lower adoption. I'm not saying I'm ready to make the switch, but at least Zig offers a different approach that's intriguing to me.