Jungle Grade System

Hey Riot, Why is it that I go plenty of games roughly 14-3 or 21-4 or something with a lot of kills or assists but I don't at least get an S-? Solely because I didn't farm enough creeps. I believe jungle should be the only lane that shouldn't matter when it comes to how much farm you have. Rather how many wards you've placed, kills, assists, etc. It's hard to farm in the jungle and keep map pressure just so I can get an S- or more. But I've gone plenty of games with much more than 15 kills and higher and only a few deaths but end up at the end of the game with 150 cs. I think this is unfair due to how much pressure the jungler needs to put on 3 lanes while the laners just focuse on csing for a chunk of the game. If you guys can change that it would be wonderful.