memcpy, strchr, etc. use SIMD. The rust HashMap uses SIMD. LLVM can and will auto-vectorize. So yes - of course Zed - "uses SIMD", but it's not a tool you can throw at everything to make it faster.
And auto vectorization isn't all that common. In many cases you need to structure your code in a certain way, in which case you're better off doing it yourself if you want the vectorization benefit.