Player Rating and the match score

I notice that the Player Rating average for my players always goes down or up significantly whenever I've been scored on or just scored a goal, respectively. I don't understand this, because the score of the match is not the same as how well the player is playing. And we all know matches where the worse playing team won the match. Is there any good reason why players ratings have to factor the score in the calculation? Or ought it be removed? Because it seems to defeat the purpose of a PLAYER rating.