Well, there can be reasons why good sales don't equal good success (depending on the definition of success). At least I am happy to see a lot of gamers enjoyed the game after the initial bugs were ironed out.
But I would add another take, just my personal opinion: I think Days Gone probably deserves a sequel more than Ghost of Tsushima. There are some reasons for it. For one: GoT is a great game without a doubt. This is a reason, because it is much harder to improve on an already good game. There is a big chance a sequel might just fall short and tarnish the reputation of the franchise. A mediocre game with good roots on the other hand might be refined into a gem with a sequel.
Also a very subjective view, but mine: I feel like GoT is more samey with other Sony games. That is nothing bad in itself, it is just that a lot of Sony games are big, cinematic, narrative driven and visually pleasing action adventures. The details may differ, so they all have their place, but as I feel it God of War, Last of Us, Horizon Zero Dawn and Ghost of Tsushima all are tapping into a similar market. Days Gone feels more sandboxy, more systemic driven. Giving that series a sequel would help Sony to diversify their lineup.
As I said, my take is very subjective, so you all probably disagree, but it is just my opinion.