Why have you forsaken me Rito.

Im here, playing Ezreal, (silver nub, please dont laugh too much) and im doing amazingly, i get most kills in the game, a lot of assists, not too much farm, but im doing well, you can see what I ended the game on. Anyway, the reason i've made this is because, even though I did considerably better than my teammates, ended on 54k damage compared to the next highest, the midlaner with 25k, more kill participation than everyone else, and I get an S-... S-.. Why.. I had 9 less farm than my mid laner.. Why do they do this to me.. Why Rito. Someone explain this to me, it boggles my mind why i got an S-, my midlaner got an S, and my support got a S+