I just realized that while the Dutch were in Taiwan between 1624–1668, and the Spanish were here from 1626 to 1642, the second plague pandemic was raging on back in Europe.
The second plague pandemic hit the low countries first in 1623–25, killing 10% of people in Amsterdam alone, and it came roaring back in the periods between 1635–36, 1655, and 1664.
The period of Dutch Formosa spans the period of the second plague pandemic in the low countries.
At the same time, the Spanish didn’t fare any better, but the worse of the pandemic hit Spain after the Spanish already surrendered Northern Taiwan to the Dutch. In 1649 the population of Seville was cut by half. In total, 1.25 million people died on the Iberian peninsula as a result of the second plague pandemic.
Could that be the real reason why both the Spanish and the Dutch didn’t control Taiwan as effective as they did other places? They were simply too distracted by more than 10% of their population being wiped out?
The little ice age was also a thing at the time, coupled with locusts and the plague. All of those things came together and brought down the Ming empire. The plague hit China between 1633 and 1644, which killed 200K in Beijing. It probably made running a colony dependent on trade with China very difficult for the Dutch.