I lost lp even though we won

about 10 minutes in after winning lane my internet shut off, roomates were moving it? I come back, we win the game. I lost 17 lp since i had been afk for 5ish minutes. Don't get me wrong, I think there should be punishment for leaving games, but if i win, i should get lp. Maybe I earn less than what i would have if i didn't afk, but if we won, why do i lose lp? I think if you afk and your team loses after you afked, then you should lose much more lp than if you lost the same game and didnt afk. But since it we won, its not like i rage quit or anything