Why Don't Game Ranks (S, A, etc) Provide Feedback?

Just played a game where my entire team was confused as to why I didn't get an S. Got me thinking that it would be much better if the game justifies its results. Essentially, how a bank presents a credit score: i.e. it would tell you where you could improve and why you didn't get a higher rank. Then we could actually know what to improve/change. Might even help people climb out of elo hell if they see that there are simple things to make them better at the game.

To be clear, I was support, went 17-8-13, had top dmg by 8k, 2nd on healing (by 600), most kill involvement (with 6 kill streak and a triple), and deaths right in the middle of the pack. My adc, with switched kills/assists got an S as did our much less involve, fewer death mid. He deserved it too, but there are so few ways I could've played that better and if I could've done something easy I'd like to know. Or at least confirm (sweeper would've probably gotten me there, I admit).