I think there's three reasons one might use Zig instead of Rust. These are just opinions, and I would love yall's thoughts.

First: there's only a certain amount of effort that one is willing to put into accomplishing one's goals, effort that will be spent on learning tools and building a project. It's not unlimited. If I just want to make a game where a character walks around the world, and I only have 20 or so hours of time before the money / motivation / market opportunity runs out, and it takes 300 hours to master Rust, that's a non-starter. If someone has 2000 hours of time available, then it'll be worth it to learn Rust before starting. If someone has even more than that, then it might be even better to use more advanced proof tools to be even safer than Rust, if safety is an absolute priority.

Second: Zig offers a lot more freedom than Rust. The borrow checker historically has difficulties with observers, backreferences, dependency references, several forms of RAII, and graphs. If one just wants a struct to contain a pointer, sometimes it's just easier to use Zig than to change one's entire architecture, which takes a lot of time and effort that one might not want to spend. Of course, this isn't a problem if one uses Rc and RefCell more, which brings its own tradeoffs.

Third: There are a lot of cases where the cost of memory unsafety just isn't that high, and Zig's mitigations are more than sufficient. For example, if I'm making a non-safety-critical app or webassembly program that's sandboxed on the client's machine and only talks to its own trusted server, that's more than enough security for a lot of use cases. In these cases, a couple memory safety bugs are just like any other bug, and it's not worth it to spend the time reducing this release's bugs from 23 to 21. This is how it was on Google Earth; the vast majority of our bugs were logic bugs, not memory unsafety (and this was C++).

Coming from Rust, the first point likely doesn't apply to you as much. The second and third points might apply, depending on the situation.

I think Rust's tradeoffs are stellar for cases like medical devices or HFT where the cost of memory safety and higher latency is much higher than your average webserver (where Go might be a better fit) or your average single player game (where memory unsafety bugs are just inconvenient, not critical).

If I was to sum it up, I'd say: Rust is pretty close to perfect on paper, when you don't consider the other human factors, such as limited time, training, or that sometimes it isn't worth it to prove memory safety. When you consider these factors, other languages can make more sense.