The following link shows the players' ranking, which countries and organizaions players represented and why they were invited.The Championship has been in China a few years now. I'm not certain for sure but I believe the way players are selected is each sub organization under the WPA send so many players (not sure that each organization sends the same number though), I believe the WPBA is also given a few seats and the host country also. This I think accounts for why there are so many WPBAers and why so many chinese players.
http://www.my147.com/News/Display.php?id=14549
The top 8 WPA ranking players were automatically invited.
Other spots were distributed among organizations and the host country , and ten open qualifying spots were available through qualifying tournament.
For instance, AAPA(Africa) only was given two spots and BCA was given eight spots.
For example, Karen corr was invited because her WPA Ranking is number one, Allison Fisher represented EPBF (Europe),
Sarah Rousey represented BCA, and Fu Xiaofang occupied one host country spot.