Two days ago I had an ARAM game where 2 players on the enemy team started arguing with each other in the post-game lobby. One of them ended up throwing racist and homophobic insults at the other and wished them to die in a terror attack.
I obviously reported the toxic player and I decided to track their account activity for the past few days to see if they ended up being banned. Unsurprisingly, they're still playing. Maybe because they've been playing every single game with at least 2 premades who probably aren't going to ever report them, no matter what they do or say.
This is way the vast majority of players has no trust whatsoever in your automated player behaviour system, Riot.