Trolls in ranked

So here we can see that our jungler went ashe jungle and the support picked a jinx support and just hid behind me all the time. Blames me for dying because she just hides. Now if the chat logs are available you can see that the Ashe said they have 7 accounts. Now my question is why doesn't riot just ban their main account because they are clearly not afraid of losing their smurf accounts.

Now I understand there are plenty of troll people in bronze too but in low gold and even doing this on purpose without being afraid of getting a ban is just ridiculous. The jinx even outright said that it's ok no ban is incoming. How is this even fun for the rest of the people that are trying to play the game?