It's getting to the limit of my knowledge here, so please don't take this as fact, however:

I believe it is because of a weird distinction between "direct" and "indirect" calls in javascript. The spec says that an indirect call is guaranteed to execute in the global context, but a direct call will execute in whatever context it's in.

The `(0, eval)` makes it an indirect call by evaluating an expression that returns the function.

I'm not quite sure about the details of why indirect calls are treated that way though...