A couple things before I really get into this. Firstly, Hokkien Chinese people are actually a subset of Han Chinese. Han is the designation for a loose set of cultural and societal traditions, but it isn’t really an “ethnicity” in the way most Westerners think. Han is extremely diverse and Hoklo people (Hokkien speakers) are just one group of many that are considered Han.

Secondly, interactions between Chinese and Filipinos long predate the colonial period. In fact, Chinese people were such consistent visitors for trade in Maynila, for example, that in old Tagalog the word for Chinese people was Sanglay, which is a Tagalization of “chang lai” or “come often” in Chinese. Nowadays the word for Chinese in Tagalog is Intsik, a borrowing from Hokkien Chinese.

So why are there so many Hoklo Chinese people in the Philippines? During the colonial period, the Spanish (as well as other colonizers such as the Dutch in Indonesia) recruited Chinese people to work in their colonies. Socially, the Chinese actually enjoyed a bit higher status than the natives, occupying a sort of middle ground in the racial hierarchy. This position actually resulted in a certain amount of wealth accumulation over time, and though Chinese Filipinos are a fairly small minority, they have a huge amount of control over economics in the modern Philippines. What also occurred during the colonial period was a lot of intermarriage between the Chinese immigrants and the native Filipinos, particularly in areas such as Maynila. A very significant mestizo (Chinese-Filipino mixed people) population resulted from this.

As to why people from Fujian were the most common immigrants. I think it is related to the poverty that the province endured under the Ming Dynasty. In previous centuries, Fujian had enjoyed economic success, in part because of overseas trade; however, the dynasty adopted a policy of sea closure and severely restricted commercial activities and the free movement of people. As a result, Fujian lost major sources of income and employment. It was only in the 16th century that this trend was reversed, with the opening up of trade once again; this brought merchant ships to China and Chinese ships (particularly Fujianese ships) to Japan and Southeast Asia. This resurgence was accompanied by conflicts with the central government and fierce competition, and resulting local wars were harmful to the province. Many Fujianese were driven overseas to find a living. Maynila was probably the most important destination for Fujian traders and immigrants, particularly during the early years of the colonial period in the Philippines, but Indonesia, Taiwan (this was the beginning of Chinese people moving to Taiwan, which was originally populated only by Austronesian-speakers), and other colonies were destinations for immigrants.

Sources:

“Up the Mountains and Out to the Sea: The Expansion of the Fukienese in the Late Ming Period” by Eduard B. Vermeer in Taiwan, A New History edited by Murray Rubinstein

Barangay: Sixteenth-Century Philippine Culture and Society by William Henry Scott

State and Society in the Philippines by Patricio Abinales and Donna Amoroso