Trolls had learnt how to abuse the system
After the troll makes the game completely onesided, they have ways to avoid getting punished by the system. They KS one or two kills to make their kda look like 2/10 instead of 0/10. Intentionally say in chat stuff like "Sorry nothing I could do" or "I am having a bad game sorry". Then they never group and just farm some jg camps to make their cs look not as bad.
That
in my last game demonstrated this so perfectly that my entire team reported him.