Didn't even bother to look at the maps, did you? Some of those bases are inside territorial waters allotted to the the Philippines by UN rules, within spitting distance of the main Phillippine islands, and also within easy striking range of Malaysia and Brunei.

Here's a diagram for those who are interested: http://www.abc.net.au/cm/lb/5464158/data/south-china-sea-map.... Note how close the China claim line extends to various other nations.