my team is trash as xxxx

today i play a game. one of the player on my team xxxx afk and this cause my team lose. why my MMR is still drop like failing from huge cliff. it is not my problem my team lose and i play as usually. but why i am responsible for this my MMR drop. its there should be some system to process or staff to balance out the cause and effect. for example someone afk. the LP and MMR should not use the system evaluate the result. instead. staff should consider someone afk and give the player what LP and MMR they deserve either + or - cause i feel this is unfair