Probably no data. China will not make data publically available if it makes them look bad.

How would they stop data from being collected by NASA satellites?

Presumably for the same reason the Gulf of Mexico doesn't show up despite having six of the ten largest US ports. I'd guess they only tracked the open ocean, but whether that's a design decision or those types of clouds don't form over certain bodies of water I couldn't say.

Either way, much of the traffic in the Pacific comes from or ends at China, I don't think anyone is denying that.