A little bias in your opinions here, my friend. Spratly islands are also far away from Vietnam as well , why should she gets more islands than everyone else. Besides, she already shamelessly and sneakily occupied more than her share already.
You need a reason? The reason is that from time immemorial, and right now, we have managed most of the island in the the Spratly Islands. We have managed it peacefully, we did not use any force to account for it, because before that no one owns any of it. So it is enough?