I'm not a Zig developer, but I imagine one reason why the Zig documentation is so spartan is because the language is still young and constantly evolving. It's really hard to devote the time and energy to writing documentation when you know that what you've written will just be wrong at some uncertain point in the future.
Many would argue that Zig is not to be considered a young language anymore. It's been out for 9 plus years already.
A different answer to that question, could be that its still unstable and making breaking changes (not 1.0), thus a reluctancy to focus on documentation to a level many consider satisfactory.
