You mean besides the 30,000 or so soldiers and airmen of the US Army Forces Far East and the gaggle of cruisers, destroyers, and submarines in the Asiatic Fleet?

The US, the Army and Army Air Forces in particular had invested a good deal of money, and manpower into their presence on the islands to bolster the resource short Philippine Army. Of those 30k men roughly 2/3 were from the US and the rest were classified as Filipino Scouts who were Filipinos who were enlisted into the US forces as opposed to their own military. The ground components on the islands when war came were built around one infantry division, and several independent battalions along with some armor units and other supporting organizations to aid the larger Philippine Army.

Meanwhile the air component was not insubstantial itself, numbering about 100 P-40 fighters, and 30 or so B-17's along with several units of older models and utility aircraft.

The Army Corps of Engineers had also constructed many quite remarkable forts and fortifications particularly around Manila Bay and the Bataan Peninsula. These included the island of Corregidor, and Fort Drum which came to be called the Concrete Battleship for its 2 14in gun turrets it sported.

The Asiatic Fleet was without question the least robust component but not without its own teeth in theory. In December 1941 it could call on 3 cruisers(1 heavy 2 light) about a dozen WW1 vintage destroyers, 2 dozen submarines of various vintages, and a score of assorted support vessels like tenders, minesweepers, and gunboats. Additionally Admiral Hart had about 35 patrol planes, most large PBY flying boats.

So I think its to safe to say the underlying premise is wrong. The US had a significant and growing force in the islands, which was specifically postured against Japanese attacks. For an Army smaller than some in Eastern Europe in the late 30's that was a significant investment of men and resources, even if it was not the most modern, or quick to receive additional forces. There just wasnt enough of anything anywhere for the US military in 1941, but the trend is clear and had war not come until Spring of 1942 several thousand more US troops, and several dozen more aircraft were slated to arrive with more potentially to follow. just a week before the war the most recent convoy had arrived from the US and a Marine battalion formerly in China had also been pulled back to Corregidor..

Now as to why they werent more successful its another question. Frankly, General MacArthur who commanded the joint US-Filipino forces and several key subordinates bungled things at the start. Despite several hours warning after Pearl Harbor, air attacks by Japanese aircraft devastated Clark Field and neutered US air power at the start of the campaign, while also damaging the naval port facilities. While defenses were attempted, radar was being monitored, and aircraft were in the air, inexperience, miscommunications, and a seeming lack of energy all contributed to failings and 50% of the aircraft on strength destroyed in about an hour. And Japanese naval superiority allowed them to chose the place and time of their landings.

Once the main Japanese landings along the Lingayen Gulf then things moved quickly. Allied forces were pushed back, often with heavy casualties. By early January Manila had been abandoned, and in accordance with prewar plans most forces had retreated to prepared positions on the Bataan Peninsula. There, in conjunction with Corregidor and Fort Drum they could resist and still deny the enemy usage of Manila Bay ideally.

As the fighting ground on into the Spring of 1942 it was clear what the end result would be, despite several Japanese attacks driven back food, ammo, and medicine were all running low. Thus on March 12th MacArthur and a few staff followed orders from Washington and left by PT Boat for Australia, leaving General Wainwright in command with orders to hold out to the end. On April 9th as the situation rapidly deteriorated on Bataan, General King the senior commander there surrendered his reaming men, and nearly 70k or so American and Filipino solders would then face brutal forced road marches into captivity in what has become known as The Bataan Death March with several thousand killed from wounds, sickness, or their captors in the process. Wainwright and the forces on Corregidor lasted another month but also surrendered on May 6, while forces in the South on Mindanao only partially surrendered and formed part of the core of a very active resistance movement across the islands.

The majority of Admiral Hart's naval forces though had long since been ordered away. Against Mac's objections the majority of his sub and surface craft had been sent South to better coordinate with the Dutch, Australian, and British forces. The majority of his subs tried for Australia. While his surface forces became part of the larger joint ABDACOM. Most then would go down fighting in a series of frantic, desperate fights in February 1942 around Borneo and the Java Sea in attempts to stop further Japanese landings.

As to the question as to why more was not done, and help did not come, it is a question of sound strategy and national priorities. In 1941 the US firmly commuted to 'Europe First' as its defense posture, acknowledging Germany as the more immediate threat and the need to keep Britain and Soviet Russia in the war. This was expanded in the Rainbow 5 war plan that called for a defensive posture and offensives only to secure lines of communication with Australia and Hawaii as needed in the Pacific for at least 6 months or even 2 years.

Earlier versions of War Plan ORANGE for a war against Japan had pictured other options. Including amongst them were things like sending the battle fleet as soon as possible to a bay on Mindanao or Leyte as a forward base to draw the IJN in and fight them there while follow on forces secured the Pacific in safety. Or sending a 'Flying Column' of fast ships to the Dutch East Indies by way of Australia to keep at least some supplies flowing to the islands. But by the late 40's it was recognized that a Pacific War would be a long slog or amphibious landings. The infrastructure for those landings, and the mobilization of reserves would take months to complete during which time the fleet could undertake limited offensives at best and was safest sticking near Hawaii or California. Thus any forces rushed to the Philippines were only adding to the sacrifice, presuming of course they ran the gauntlet of Japanese bases in the Mandate Islands, and the large fleet base at Truk.

Inter service feelings were of course not aided by feelings of potential abandonment and of course strategic plans were not often communicated to the grunts. But in the end even before the battle line found itself blasted and sunken at Pearl Harbor there was not going to be any cavalry coming, to risk the battle fleet before the supporting forces for a sustained offensive could be mobilized would be to risk giving Japan total dominance in the Pacific for years until a new fleet could be built.