Earlier episodes made it pretty clear as to why Sawyer might have chosen to stay on island- like Ben said, Sawyer wouldn't be much off the island while he's somewhat of a useful, strong guy slowly gaining power and popularity among Losties.

Jin stayed, probably because there weren't enough space or something like that, and he ended up having to make a sacrificial choice for the good of Sun and the baby.

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"Bear...? Is that you?"-- Hurley S03E4