Why do we lose lp for losing a game where someone afks?

I have had this happen only a couple of times, but the question has just dawned on me. Why do we lose lp for someone going afk in our ranked games? Personally I dont think its fair that I lose the same amount of lp for a fair 5v5 game as an unfair 4v5 game. (Especially when that afk is your adc or jg.) Being punished for losing my game due to whatever problems my teammate(s) may be experiencing with their internet, pc etc. is honestly unfair and is just a constant setback for many of us who trying to climb out of "Elo hell" or just get into a higher rank than what we were in before. I dont ask for a complete removal of the lp you would lose, but at least halfing it. I get it, if you beat your opponent somehow with said handicap, they lose lp and you will gain, but its not like you're gaining anything extra.