I played a game of ranked where 1 of my teammates was trolling/nading us which caused my other 2 teammates to leave. Why am I still getting deducted rank rating over that shit?

I know this is an extreme case of getting assists but the fact that I was able to topfrag just because i had a lot of assists(mostly from util) despite having 7 less kills. This is why I enjoy playing support and still rank up. I hope this...