Weather forecasts in Hong Kong are hit and miss this time of year add to that the massive amount of traffic and holding once a few storms rock up . Change of runways and airspace constraints only add to the problem . Macau is just a 3 rd runway at Hong Kong . Shenzhen , Guangzhou and Macau regualary have storms but Hong Kong is clear ( hard to believe ) ? Do you want to rock up to Hk with no alternate ? Do you want to take 300 passengers with no CHINESE visa into China on a diversion only to run into FTL problems ? Diverting into Manila is understandable but carrying Manila plus 30 for Hk makes more sense .