Kirkman cites creative differences in handling properties as why he’s disappointed in Martin.
In regard to his and Martin’s respective roles with their franchises, Kirkman serves as the co-author of the “Walking Dead” comic books, as well as a co-creator and an active writer of the TV show. By comparison, Martin acts mainly as the author of the source material for the franchise he created, though he has also written four episodes of the HBO series.
But both creators have reached sticky territory as the shows run alongside the production of the source material and, in the case of “Game of Thrones,” outpace the novels, creating a dilemma with how each series should move forward with both wanting to adapt and possibly needing to just make it up. While Martin has had some trouble navigating that, Kirkman has a firm opinion on the matter.
With that kind of philosophy, it makes sense that Kirkman would disagree with how Martin has approached his situation, telling three canonical secrets to the producers before the respective books came out, as Martin seems to be more lenient about the interplay between his multiple entities than Kirkman would ever be.