When you create a custom character, he gets inserted into the world out of nowhere. He never existed before and now he does, and that makes all interactions with that character unfulfilling, unnatural and out of place because it's impossible to fully take into account all variables of your custom character: race, sex, face, hair, (often poorly written) backstory, skill set, etc. Instead of having a well established protagonist with a decent backstory and character we end up having a bland and generic nobody who doesn't stand for anything and represents nothing like it was with cyberpunk, which by the way would be a much better game if it had an established protagonist. Out of all games with character creation only DOS 2 managed to create a decent story, and even then the game feels much better if you choose to play as an established character instead of creating your own. On top of that, in that particular game it worked because the lore of the game isn't focused on any particular individuals but rather on the universe as a whole. In our instance the series is literally called "The Witcher" and it has always been about particular characters and their stories, not as much about the world. Aside from DOS, I can't recall a single game with character creation that has a decent story. They may have other advantages like replayability, but The Witcher games don't need those advantages if it means sacrificing narrative because narrative is the cornerstone of this franchise
Peace 
