Seems to me what the Freighties and their associated Losties have been
working on is to provide an excuse to be stuck in the vicinity of the
island for a time, to remove some of the Losties, and then to sail
away with them. They supposedly came for Benjamin Linus, then they
ostensibly were plagued by insanity and resulting sabotage, and
eventually they'll be "forced" to pull away. It's all fakery, of
course.
Robert