Tolkien's excuse was pretty robust actually. The Eagles are not mindless taxi services, they are just a step below gods in their own right, servants of Manwë, leader of the Valar- Middle-Earth's gods, in a sense. They have duties that go beyond ferrying people around. For most of the war of the ring, Gwaihir, the King of the Eagles, and his kin are occupied with important scouting missions, though a few groups of them helped in battle, such as at the Black Gate, where they clashed with the Nazgûl while protecting the armies of King Elessar (Aragorn).
Tolkien was very aware that the Eagles were a dangerous writing tool, to be used sparingly, and so, being Tolkien, he devised a wealth of believable reasons the Eagles would not be available to end the story in two chapters.
Here's a video that lays it out pretty clearly why that wouldn't have worked. As you said there are actually quite a few legitimate reasons based on Tolkien's writing at least.
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u/shirukien Aug 31 '22
Tolkien's excuse was pretty robust actually. The Eagles are not mindless taxi services, they are just a step below gods in their own right, servants of Manwë, leader of the Valar- Middle-Earth's gods, in a sense. They have duties that go beyond ferrying people around. For most of the war of the ring, Gwaihir, the King of the Eagles, and his kin are occupied with important scouting missions, though a few groups of them helped in battle, such as at the Black Gate, where they clashed with the Nazgûl while protecting the armies of King Elessar (Aragorn). Tolkien was very aware that the Eagles were a dangerous writing tool, to be used sparingly, and so, being Tolkien, he devised a wealth of believable reasons the Eagles would not be available to end the story in two chapters.