Here’s a couple of ideas–they both require feathers (writing quill) to fly (freedom), or they both have the last word as in the raven being a messenger from the other side, and our ability to always say with finality what we want to say in the written word. Just something to wonder about.
Why is a raven like a writing desk?
The point is that the riddle was asked by a madman (the Hatter), who expressly said that he had no idea what the answer was, so there’s no reason to doubt the Rev. C.L. Dodgson when he said, “the Riddle, as originally invented, had no answer at all.”