> I don't understand why Zig's `Io` is a "monad".

I don't see how it's true in any meaningful sense. It seems about the same as stating that any function is an example of the reader monad.

The whole point of monads in programming languages is as an _abstraction_ that allows one to ignore internals like how the IO token is passed around.

Maybe Zig is a language for people who are scared of abstraction. Otherwise they'd presumably be using something more powerful like Rust.