LogFAQs > #977087763

The only reason why the eagles were even able to show up in Mordor when they did is because Sauron and his armies were focused on what the armies of men were doing. If he hadn't been distracted, the Nazgul would have been sent out as soon as the eagles were detected. I don't know enough to say which is more powerful, but I suspect they're about evenly matched and it would be a great risk of delivering the ring right to Sauron if the eagles failed in their mission, that's before we even bring up the possibility of orcs just shooting them down.

The eagles are servants of the Valar, the same beings (gods, really) that bound and banished Sauron's master, Morgoth, from the earthly realm. There'd be no faster way to kick the Mordor hornet's nest than to send a bunch of eagles that way.

And if they should pass anywhere near where Saruman's spies were watching, Saruman might even give Sauron a head's up that they were coming.

There's also the possibility that the Valar would simply refuse the eagles permission, either because they're concerned about them getting corrupted or they just don't want to interfere. It's like how Gandalf is of the same race as Sauron and comparable in power, but rarely uses it because that's not what he's there for. He can persuade, but not just cast spells on people and force them to do as he pleases.