Like I said. To my memory its established that the eagles aren’t a possibility for various reasons, just more subtly than having Gimli shout “Of course we can’t use the Eagles! They’re all drunks and we can’t trust them to fly a straight line”. Explicitly explaining plot points is not good writing, and neither is attempting to explicate why each and every possibility wasn’t followed up on.
Besides to that point in the book it’s not as if there is much to indicate the Eagles are much of a thing to begin with. Many other characters float in do some crazy and don’t drive the fellowship directly to Mordor. Why doesn’t Tom Bombadil, who is immune to the ring, carry it to Mordor?
In the deep cuts the Eagles are basically the Watcher from Marvel Comics, they’re supposed to keep an eye on things and report back and not interfere. But like the Watcher sometimes they break the rules in small but critical ways.
And again: Aerial assault by Eagles is not exactly subtle. You might remember that Sauron has undead soldiers who sometimes ride giant flying monsters. Something that’s well accounted for in all the talk of hiding the ring from Sauron along the way, without info dumping about what the eagles are and how Sauron has flying zombie generals.
Why didn’t they go around by boat?
They could have dropped in much closer to Mordor and an unexpected direction. Saving a lot of time, trouble and suffering. The elves are even famous mariners with very impressive ships.
