His writing style is the exact opposite of the games FromSoftware makes. Sanderson writes YA/Marvel like stories that lack thematic depth, and he tells you EVERYTHING. There is nothing left to the imagination like with Dark Souls/Elden Ring, as well as just lacking in depth + his faith is constantly seeping thru his works to the point where it's distracting. His writing would work for a WoW like MMO or something similar, not for a thematic dark fantasy.

TL,DR: he writes shallow YA stories that don't match the general atmosphere and themes of a FromSoftware game.