Sure it wasn't released in 2019 but, in my opinion, it didn't have enough time on the market to be considered for ?Game of the Year last year. The Game Awards were held a couple of months after it's release, while God of War was realeased back in February of 2018, it had the better part of a year to get into people's homes and had enough time for players to experience it completely.
RDR2 is an awesome game, but in my opinion it shouldn't have been considered for ?Game of the Year because of the low market time it had in comparison to the other games nominated. Same goes for Marvel's Spider Man. I'd put RDR2 and Spider Man as my top 2 games of 2019.