That's only because, for once, they hung a lantern on it.
SPOCK: Colloquial twentieth-century English. An amazing parallel.
Which, again, is exactly the problem. For one thing, it proves that the aliens in other episodes are not actually speaking English, otherwise Spock wouldn't have been amazed. For another, calling explicit attention to the conceit just underlines how nonsensical it is, without actually providing an explanation for it.