Because God of War hit all the notes. Top-tier graphics, fantastic story and characters and great/fun gameplay.
I had the most fun with Octopath, but that's because it was comfort food for me. It was impressive for what it did with pixel art, but it didn't move the industry forward in the same way as God of War or Red Dead.
Hollow Knight was an awesome indie, but not drop your jaw amazing like GoW. It's also not a 2018 game.
I wasn't really trying to make a case for Octopath or against God of War, but pointing out that the 'matter of fact' quality of the GOTY nod is strange for that poster and, at the time, for myself.
Having enjoy other gamed more, it's weird to say GoW "deserved it" more. I don't think it did.
Because the odds were totally against this game before the release. All the games you mentioned were either totally fresh and came out of nowhere or you knew exactly what you would get from. With God Of war people were really sceptical and it is not every day that a well known IP changes so drastically and even get better than before.
I really don't believe the odds were against a massive budget AAA first-party Sony title with years of hype.
Sure, some people beholden to the IP were skeptical they weren't foing to get what they wanted from the series, but more people - like me - thought GoW was a average action game with an unfortunate level of edginess and welcomed the change. Nobody really thought it would be a
bad game, and, because our hobby is obssesed with blockbusters, many had it pegged for GOTY well before it launched.