It’s maybe because the Spanish colonial strategy was to undermine the native oral tradition by substituting for it the story of the Passion of Christ.
The existing literature of the Philippine ethnic groups at the time of conquest and conversion into Christianity was mainly oral, consisting of epics, legends, songs, riddles, and proverbs.
Among the only native systems of writing thathave survived are the syllabaries of the Mindoro Mangyans and the Tagbanua ofPalawan.
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In that period the church authorities adopted a policy of spreading the Church doctrines by communicating to the native (pejoratively called Indio) in his own language. 
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