Why is this game giving so much power to trolls?

One premade troll botlane can just make the whole game unwinable but at the same time keep the whole team hostage by just voting no on surrender, because of some reason 3 out of 5 is still a lost vote.

Why is RIOT allowing trolls to have so much power? And if one of the trolled players goes AFK, BAM report and BAN for AFK!