losing lp

So the short story. I was playing jungel tank in ranked, and our bot lane was dying and feeding alot while they were flaming more than an forest fire. They later mid game just left the game after another and we played 3 v 5 for about 10 min.

can someone explain why i still lose 19 lp and not like 17, while losing a game with 2 players afk? shouldn't you get somekind of compensation for players leaving in a ranked game? this just makes me mad.