Hainan Island is closer to the equator and closer to the coveted 460m/s Delta Vee earth's rotation provides.

And also next for the Chinese is a newly developing booster capable of parking
upto 25 metric tons into LEO...25 metric tons would mean both manned circumlunar
navigation capability for a two-man ship, and a Salyut-class spacestation.
The Salyuts were only 17 metric tons; 25 metric tons in orbit woul give the
Chinese more flexibility regarding spacelab/spacstastio development.
cheers.

Jake

It would be nice if the Chinese started launching a manned mission every 4-6 months, instead of one to two years