Note: IANAL

Copyrights already preclude short phrases for the same reason -- there are only so many ways in which short phrases could be produced. The moment a work becomes larger (large enough; AFAIK, the threshold is not precisely defined), the reasoning you applied fails to apply.

The Google-Oracle lawsuit did not decide whether APIs (when large in number) are copyrightable or not.

Let me get this straight: Since there are only so many ways to write a for loop, you doubt that for loops are copyrightable. From this you conclude that code, in general isn't copyrightable?

That's like saying "there's only so many ways to greet your neighbor, so any text that simply greets your neighbor isn't copyrightable – and therefore no text is copyrightable".