going to happen onscreen in the show, and I'm fine with that.

I think it's part of the difference between a book and a television show - RJ uses a lot of words to describe things, and give history, that would be pretty boring just watching on a television screen. I think they're using Logain as a way to introduce some of the expository information to the audience in a visual manner.

Plus, Alvaro Morte is a relatively big name actor, and it's hard to keep a significant actor for a significant character tied up when he's in season 1, but then not much more relevant until far later in the series. Expanding Logain's story will help keep him in the show throughout the seasons.