Okay, since I am being an asshole I will answer this seriously, and give my thoughts.
Because this is better than doc review.
You did see enormous population movements during this period. You belittle 33,000 people in Batavia, a few thousand people in Manila, etc. But these are significant population movements given that most of the settlers came from Fujian and Guangdong, China's coastal provinces where most maritime trade derived from.
This is why I am being snarky incidentally. Comparing "China" in terms of population movement to the UK makes no sense given the size and regional disparities involved.
You saw even greater movements within China; it's been estimated that 75% of Sichuan's population was made up of settlers in the 1720s, for instance.
So, why didn't they go overseas even more than OTL?
A big reason was that it wasn't secure. The Batavian, Manilan, and Muslim Southeast Asian histories are replete with massacres of Chinese whenever they got uppity or the local authorities wanted a scape goat; in that context, why bother settling abroad when you could move somewhere closer to home? Moreover, the state didn't want people going abroad. In the Qing, this was tied into South China's opposition to Qing rule, exemplified by Koxinga, the dude who took Taiwan from the Dutch.
You see this in Qing sources; the emperor had no problem with massacres of Chinese settlers in Jakarta, because they'd left China; but merchants who resided in China and just travelled there to trade were under imperial protection.
Given the population movements in OTL's China's history during this period, a stable place to settle overseas would have likely resulted in population transfers on a significant level.
Now, before we chastise the Qing as backwards and making the "wrong" choice, let's remember that it was the overseas Chinese who overthrew them in OTL...