Why did the USA wait so long to help American POWs in the Philippines?

I never even knew about the amount of American and Filipino prisoners of war the Japanese held during ww2 until today and seeing a one hour doentary about their rescue. However it is bothering me a LOT that the US government abandoned its own men and made no attempt to rescue them for YEARS when thousands had by then died HORRIFIC deaths, and concentrated their efforts in europe. What was going on?! Anyone shed any light?