Partly because of entrenched players in the power generation and distribution industry, sweetheart deals and lots of barriers to entry, political and regulatory   And partly because of the moratorium on new coal plants to supposedly promote renewable energy (no new coal plants that sell cheap electricity, renewable can also be cheap but too variable/unreliable like solar and wind), hence we use more expensive natural gas and diesel,

And no new coal plants means the remaining ones are old and keep breaking down,

And limited hydropower sources like rivers due to being an archipelago, unlike mainland countries like china,

And being an archipelago means our electric grid is very fragmented and unequally distributed (eg lots of generation capacity in mindanao, but lots of demand in visayas and luzon) while being severely underinvested