I am wondering why Tagalog is not mentioned (there is a Tagalog Wikipedia).
Though I am certain it's correct that a significant number of Filipinos
speak/write sufficient English to edit (and some of them may not even
know Tagalog), it would seem possible many people might prefer editing
in their mother tongue
I suspect a bunch of reasons.
English is actually an official language of the Philippines, and taught in school. Despite the fact that people in Philippines might be secondary speakers, they're potentially a good group to invite to join a geography-specific WikiProject. Unlike targeting say, a U.S. state, the population to draw from is enormous.
To my understanding, Tagalog Wikipedia suffers from confusion and conflict over which orthography to really use, which among other reasons keeps it small. This was one of the smaller projects studied as part of the WikiHistories undertaking, and there's more detail at https://meta.wikimedia.org/wiki/Research:WikiHistories_fellowship/Tagalog#Language