GANDALF CAN’T JUST ASK THE EAGLES FOR HELP ALL THE TIME
As one of the Istari (powerful wizarding servants of the Valar), Gandalf had an understanding with the Eagles, also sent from Valinor, that they were all on the same side. Both Gandalf and Gwaihir, descendant of the greatest Eagle to ever live, were delivered to the lands of Middle Earth, but neither were greater or more kingly than the other. This presents a gaping hole in the argument that Gandalf could’ve simply asked the Eagles to carry the One Ring to Mordor, as the Eagles are not under Gandalf’s umbrella, nor are they a taxi service to the Istari.
YES, THE EAGLES DO HELP SOMETIMES, BUT IT’S UP TO THEM
Gandalf the Grey had saved Gwaihir the Windlord from a poisoned arrow, thus creating a lifelong friendship and bond between the two. It wouldn’t have been kind or respectable for Gwaihir to ignore Gandalf’s plea for aid in The Hobbit , and these Eagles are as proud and proper as they come. But, this does not mean that the Eagles would swoop in for just any of Gandalf’s requests. Again, they do not directly serve anyone but the Valar.
We also see Gwaihir swoop in and save Gandalf from Saruman’s clutch in The Fellowship of the Ring , but this is yet another situation in which aiding an Istari was of little to no consequence for a Great Eagle, different from putting themselves in great danger by flying above Orcish grounds and into Mordor. The Eagles are blessed, but not indestructible.
GWAIHIR PHYSICALLY CANNOT DROP THE ONE RING INTO THE FIRES HIMSELF
The Eagles of the Valar are huge, and that’s an understatement. Not only would their flight above Mount Doom cause a stir in Sauron’s forces, but there is no physical way for Gwaihir to drop the One Ring precisely into the Cracks of Doom. Not just into the fires of Mount Doom, you see, but in the exact spot in the mountain where the One Ring was forged. Someone must enter the mountain itself, approach this exact volcanic fissure, and throw the ring into the fires there.
MANY SPIES HAVE MANY EYES
Small and quiet, yet adventurous and loyal, hobbits were the perfect choice for sending out on this treacherous journey. Though spies of the enemy knew of Frodo’s quest, the focus of forces from Isengard and Mordor was split as they fought against Rohan and Gondor, thus leaving Frodo and Sam to follow a path by which they could move along mostly unseen.
Even if one of the Eagles had carried Frodo or Gandalf on their back with the purpose of entering the mountain, Sauron’s spies would be able to spot them at just about any moment, and attack. There’s no hiding when you’re an Eagle of the Valar and are flying straight into the mouth of evil.
THE ONE RING IS TOO POWERFUL FOR THE ALREADY POWERFUL TO POSSESS
We’ve seen Valar-blessed beings in the presence of the One Ring, and we’ve witnessed their sinister reactions to the power they could hold if they were to take the One Ring for themselves. An enormously important factor in having a hobbit carry the ring was to take advantage of their goodness, and hope that they would make it to Mordor before the ring-sickness set in.
