When I've read and watched documentaries about the Battle of Samar, I've been told that Taffy 3's small force of CVEs, DDs, and DEs was the only Allied naval force which stood between Kurita's battleship fleet and the Marines on Leyte.
But by the time the Battle of Samar started, a few hours had passed since six battleships of the 7th Fleet had routed the Japanese Southern Force in the Surigao Strait just a short distance away. Where did these battleships go after that battle? Were they not in the Leyte Gulf and in a position to defend the Marines in the case that Taffy 3 had not been able to stop Kurita's advance?
After the situation became clear Oldendorf was ordered by Kinkaid to head North, and then to serve as a secondary line to block the actual entrance to Leyte Gulf from the North East, and then back North before the battle ended.
The first thing we should note is that Taffy 3 was far from alone. Unlucky in that they were the most Northerly force and first to come into contact with the enemy, but not alone. As the number indicated they were the 3rd of 3 task forces of escort carriers and screens that were tasked with providing air support to the landings and some auxiliary air cover and ASW patrols to the anchorages and fleet train off the beaches. The overall command of TF77.4 was that of Thomas Sprague(no relation to Taffy 3's Sprague though) he was also the commander of Taffy 1. Taffy's 1 and 2 did come to their peer's aid with additional air support during the battle as Taffy 3 attempted to retire towards them while also masking themselves in some handy rain squalls.
The other major issue is timing and distance. Oldendorf with the old battleships in 7th fleet was well over 100nmi of steaming from the Taffy's. His force had first blocked the Northern entrance of the surigao straight while the Taffy's were off the North East off the island of Samar itself. Even if we credit the gunline and escorts with being ready to sail to Sprague's aid right away at about 700am when word starts to get out about Kurita's force the best realistic speed they might achieve is 20 knots and even that is generous really. So 4 hours or so is probably the best ETA under ideal circumstances, with the battle continuing to drift South towards them. But the force was in no way ready to sail to the rescue at the drop of a hat. The escorting forces of destroyers and cruisers had pursued and mopped up some distance to the South and had to reorganize, several were damaged or sunk as well. And while the battleships were only firing for about 20 minutes(from 0350-0410) were still somewhat unsure of the actual state of the enemy after a night of hot action. All they had to go on were rough radar pictures, occasional visible explosions and conflicting and confused reports from their escorts. Only scout aircraft with the coming of day could confirm the existence or not of an enemy force still in the South. So if Kinkaid still believed Halsey was guarding the Northern flank and would be swooping down on Kurita it would at least to him seem dangerous to unguard his Southern flank to redeploy.
We should also note that Kinkaid did indeed try to figure out where Halsey's ships were asking even as the gunline ceased fire at about 0415 to Halsey where TF34 (his provisional force of fast battleships and escorts), not receiving his reply until just after 0700, so at the same time that Kurita's force was spotted and opening fire on Taffy 3. And indeed Oldendorf was ordered at about 0730 to get what ships he could heading North to Sprague's aid. And had Kurita not broken off the engagement at about 930 it is very likely that the 7th fleet battleships could have gotten into the action later that day, or Willis Lee and his ships gotten them in the evening, night, or next day as a dual effort. Kinkaid also flip flopped a bit with what he wanted Oldendorf to do, between 830 and 900 he had the battleships and some escorts headed North then was ordered to serve as a another blocking force as he had the night before, then reversed himself and wanted the ships headed towards Sprague again. All the while the ships had been at General Quarters for going on 14 hours, and while ammo was still in good supply many ships would need to refuel soon which limited tactical options as well.
As with most of Leyte Gulf a lot of the answers rest in poor communication and worse organizational structure. By having 2 different full fleets with different missions and different direct superiors and great distances involved it created many potential points for issues. Kinkaid in 7th fleet answered to MacArthur who was ashore, Halsey answered to Nimitz at Pearl, and Halsey tended to operate with a great amount of leeway he had built up with Nimitz, that Nimitz would so positively get into the particulars of how Halsey was fighting the battle(his specific question about TF34) show how dire the situation was felt to be.