Firstly, I just assume everything affects the players' performances. We can't prove otherwise, so it's a lot less hassle to do this.

Secondly, I find attacking players can lose moral if they don't score, even if the team wins. #selfish

Thirdly, the chances of winning goes up if your team is better than theirs but isn't guaranteed. You can be >20% worse and win or >20 better and lose:

That's football.