Beyond the given reason as to why Roathe enjoys the company of the Cavia, I believe he particularly enjoys conversing with Bird-3 because Bird-3 is existentially curious. This is something he and Roathe share.
Roathe wants to get to the heart of any matter, regardless of pretense, and it's why Bird-3's curiosity and perceptiveness intrigues him. Roathe loves to wax philosophical and greatly values these traits in a conversational partner. It's also why he can become short with The Drifter if they refuse to entertain a thought or idea with him. Roathe wants to play in the conversational mud, and he's able to do that with Bird-3.










