In the Philippines there is a racist caste system in play that demarcates and stratifies individuals.
This caste system is not only found the in the Philippines it's also found in other countries which were formerly Spanish colonies; countries like Argentina, Peru and Mexico.
This is system is called a Casta and it is often observed that an individuals race reflects his/her social prestige. Below is a list of the divisions of the Casta arranges according to rank.
THE SOCIAL DIVISION IN THE PHILIPPINE CASTA
Persons of Spanish or descent born in Spain
(i.e. from the Iberian Peninsula which led to the name). They were considered so much higher than other castas that many women went back to Spain to give birth.
They are the elite and they held important jobs in the government, the army, and the Catholic Church, and usually did not live permanently in the Philippines. This system was intended to perpetuate the ties of the governing elite to the Spanish crown.
After Philippine Independence their unholy kind was persecuted and removed from these hallowed islands
This term was used to identify people of Spanish ancestry, but born and living in the Philippines. The Filipinos are the upper class of the society. Many Filipinos owned businesses or haciendas and were very wealthy. They occasionally had government jobs, but they were not respected by the peninsulares. During the Philippine revolution the term was expanded to incorporate all peoples living in the Philippine archipelago which included the full or mixed Chinese, Hispanic or Indian residents and the mainstream Malays, in modern usage however the term "Filipino" became synonymous with the indigenous Malay peoples that form the bulk of the population.
Originally this refers to a persons with one peninsular parent and one indio parent. Mestizos are considered the middle class of Philippine society, however during the course of Philippine history in the face of historical demographic shifts such as the mass Chinese migration to the Philippines, the presence Latin American traders (due to the Galleons), the arrival of Indian money-lenders, the invasion of the United States of America and the occupation by Japan the term was expanded to encompass all Filipinos with partial foreign and native ancestry.
Like in Latin America, the term "Indio" refers to the native inhabitants. Often the unmixed Malays were called Indios, this is considered deregatory; they form the mainstream demographic slice of the Philippine islands. They are often abused and are drafted for slave labor. Such is the case of the Cavitenyos whose general population often starved or went bankrupt due to the slave driving of the penninsulares in order to create the famed Galleons.
They are the dark skinned aboriginal people of the Philippine islands, they are disdained and ostracized due to their black skin.
So basically the answer to your question is this: It's just plain old contempt fostered by 300 years of racist rule.
Hispanics who come from Latin America that are now Philippine citizens are often mestizos but the mestizos are of lower social ranking compared to the Penninsulares, the pure blooded slave masters of the Philippines!
Hence they often hide their Indio blood and masquarade as full born Spaniards inorder to avail of the sense of superiority over the lower castes