Asia's 9 busiest airports in 2019
https://edition.cnn.com/travel/article/asia-busiest-airports-2019/index.html
When I see the airports listed here, I found that Guangzhou Baiyun International Airport is close to Hong Kong International Airport, both of which are in Pearl River Delta.
It means how the area is economically huge. We can understand why Chinese government is promoting to integrate the area by opening transportations.