I think it would be easier to spot an Indian, Egyptian or African illegal migrant in Hong Kong, so I guess they can take the risk. Whereas the mainland Chinese will blend right in with Hongkong population. You know how all the Asians look the same and all
j/k
Vietnam has visa-free entry to singapore. They can blend in easily and become illegal immigrants. They infact, do do so. More South Koreans are illegal immigrants than Chinese are. Yet they have freeer passport requirements. 50% of Nigerians want to leave their country. Nigeria's passport is better than the standard PRC one.
China does not have visa-free entry.
Vietnam's GDP/capita is less than 4x that of China's.
You know what the problem is?
Our government, and racism. Probably government 70% racism 30%. PRC, ROC and HK all have higher than average visa requirements, that's the racism part. It's not all racism though. Through PRC lobbying (Hong Kong doesn't even have a foreign affairs office), 100 countries admit PRC (HK) passports without visa. 3 did in 1997, an increase of over 33x. Our government has not moved at all on mainland private passports. Getting a passport is also hell, requiring a trip to Beijing in person, processing time of 40 days and you have to pay for the mail. Even for travel into VISA FREE/VISA ON ARRIVAL countries like Malaysia and Indonesia, it's not their border controls that will get you, it's our internal ones: they check your passport for a stamped Visa, or they won't let you board the plane!
Getting a visa to India? Forget about it. Processing time is over a month and you may be denied for any reason or no reason at all. Visas for India into China? 4 days processing. Huawei projects in India were cancelled (to the detriment of India!) due to visa problems before. In fact, the passports of NORTH KOREA and ZIMBABWE are superior to the visas of China - visa free entry to singapore and HK respectively.
Why do they do this? Well, face issues. Japanese citizens can live and work in mainland China better than Chinese ones can (including HK and Taiwan!). Another reason why rescues of PRC citizens in times of crisis is so efficient, but when you get arrested for troubles overseas, the consultate hardly ever sends a lawyer to help you! This is the downside of an authoritarian government - they can get away with blatant discrimination and incompetency.