[wongarsu]

Taiwan is just 150 miles / 250km from the Chinese mainland. You can just use a regular airfield. When talking about the island chains around Taiwan you get a bit further out, but nothing you can't handle with one midair refueling.

On the other hand if China were to prepare for a war in the South China Sea aircraft carriers would be very useful. They have a couple airstrips there, but they are vulnerable and not as flexible as bringing a couple carriers to the coast of your enemy. It's also a good deterrent as a pure show of force.

Keeping the Malacca Straight open might also be a big part of it.