Why is a player with a history of trolling not banned?

I went on a losing streak, last game of the day, I get a "troll". He is queued in as support but picks ADC champ... (probably picks ADC or fill, and goes ADC no matter what).

So people ask him, does he really want ADC, others will support then... Doesn't say a word entire lobby.

Fast forward into the game, doesn't say a word, doesn't leash, goes straight to bot lane & goes straight to enemy tower like he wants to fight them at lvl1 under tower...

15:00 mark, instant early FF, then he begins to FF everytime his cooldown is up. He is 0/5/0... I look at the way he plays, he isn't very good to be in that games MMR.

I checked his history, all losses, all negative KDA, most games ending in 20 mins or less (probably because his team realized he's trolling).

The game I played with him was his final placement game. Guess what he placed? GOLD 2. Even after losing all his placement , and looking like most of them were FFs.

If he isn't a troll, his skill level doesn't match the MMR he is in. So why is he here?

If he is a troll, I am 100% sure everyone in those games reported him, so how is he still not banned?

Also he did not have a border, but yet if he's new to ranked why is his MMR so damn high that after 10 losses where he has a horrible KDA he still places GOLD 2? It makes me think he was very high last season but was then punished for some reason and had his rewards removed. So how is he still here playing and why is his MMR so damn high???