Not few. Just not many in international competition.
The big problem is money. Given that our money is worth bupkis elsewhere, it's hard for a Philippine-trained driver to get enough in terms of local sponsorship money to go out racing.
Hell... most people can't even afford a car around here... racing? SCCA-style club racing may be a middle-class sport in the US, but here, it's reserved for the rich or the insane.
The last time Filipino drivers featured prominently in international competition was in the 60's and 70's, when the economy was actually at par or better than countries like Japan and Singapore. Nowadays, we hardly have the money to run a local touring car series, and attempts at open-seater series like Formula Ford, which help train drivers for more rigorous forms of racing, have yet to bear fruit.
There is some hope... there's a team featuring Gaby Dela Merced that makes the trek to the 25 Hours of Thunderhill every year, and they're doing pretty well in the series they've entered. Of course, the fact that they have a driver who's kind of cute helps in terms of the sponsorships...
That's all there is to it. Money. Without it, we won't even know whether there's a vast pool of untapped talent or if all Filipino racing drivers are hacks.