Spiderman is the most popular superhero. No matter what you think, he's more popular than Batman, Iron Man and Captain America. The game is pretty good and has pretty graphics which makes it appealing to the masses. Its open world while God of War is linear. Spiderman is a standalone game and not a sequel to a long lineup of games like God of War so there is no story catching to do for new players.
On top of that, Avengers Infinity War came this year and Spidey had a major role in the film. It made 2.2 billion dollars. He died in the most tragic moment in the film. Many people are just happy to have him again, alive in a game.
There is too much reason for Spiderman to sell more. On top of all this, God of war is a niche series in UK and japan, the only countries where we have any data. Its mostly popular in North America, Latin America and the BRICS countries.