Riot fix your broken game please

Lost 4 games in a row and deranked because of trollers or afkers 1 game: Mid went 0-5 in 5 minutes. 2 teammates dived their mid at lvl1 and died. Support just rushed and died all the time. Only me and adc played well. 2 game: adc went 3-18 (only 3 kills that were all low enemies) and had same dmg as enemy Braum. Me, jg, supp and mid played well but we lost because Twitch got fed to 30 kills. 3 game: Teammate got autofilled to support so he just refused to play support and played adc stealing farm from real adc and running in middle of them all the time ending up with 2-14 (also only low hp enemies killed) 4 game: Jg and adc went afk at 5min so we lost.

Can someone explain to me why these people are not getting banned and why does it affect MY SKILL level if my team is trolling/afk/very bad?