It mainly comes down how the std is designed. Zig has many good building blocks like allocators, and how every function that allocates something takes one. This allows you to reuse the same code for different kind of situations.
Hash maps in zig std are another great example, where you can use adapter to completely change how the data is stored and accessed while keeping the same API [1]. For example to have map with limited memory bound that automatically truncates itself, in rust you need to either write completely new data structure for this or rely on someone's crate again (indexmap).
Errors in zig compose also better, in rust I find error handling really annoying. Anyhow makes it better for application development but you shouldn't use it if writing libraries.
When writing zig I always feel like I can reuse pieces of existing code by combining the building blocks at hand (including freestanding targets!). While in rust I always feel like you need go for the fully tailored solution with its own gotchas, which is ironic considering how many crates there are and how many crates projects depend on vs. typical zig projects that often don't depend on lots of stuff.
1: https://zig.news/andrewrk/how-to-use-hash-map-contexts-to-sa...
