Honestly as long as players are forced to play a game being unable to surrender unless 4 people hit yes you're going to have a lot of toxic players. Being stuck in a game at the mercy of 4 other players is a very powerless experience causing people to become irritated and therefore toxic. That one person being toxic can then either infect (so to speak) other players on their team or can even spill over into that players next game (such as they go in already mad so are toxic straight from champ select). As you can see the pattern of this happening causes a large portion of the community to be toxic at some point.
Riot's response to this reaction of being toxic is "punishing" players or straight up banning their accounts and putting this power into the hands of the player base with an automated report system. This however does not solve toxicity and only creates more. First of all, they are giving toxic players and trolls the tools to "bully" teammates and threaten with reports causing those people to themselves turn "toxic" as a defense mechanism and this further irritates the toxic players into becoming more toxic. Then, the players that get banned most of the time make new smurf accounts and come back even more toxic do to riot removing their old account, taking away all paid for skins and such (that players bought with real currency) and making them have to re climb and re unlock champs intern making the already irritated and therefor toxic people more irritated and therefor more toxic. And the third thing the report system does is make players instantly try to threaten and fight with eachother over "im going to report you" and "imma get you banned" for any little thing rather than trying to get them to work together. This only creates a more hostile and therefore toxic environment that players are stuck in since if the leave they get reported.
So all in all its a catch 22.
