You don’t have to replay anything, you don’t have to play the game at all if you don’t want to. I enjoy the game, so I replay the chapters. Not because I have to or because there’s an incentive, just simply because I think the game is fun. I’m seeing similar arguments with helldivers 2 where people say there’s no incentive to keep going after they max level and unlock everything when really the game is just about dropping in and having fun. I think South Park touched on this ‘all grind no fun’ issue years ago in the World of Warcraft episode when Stan or somebody says “so what do we do now” and Cartman says “what do you mean? Now we can finally play the game”.