Self control for fear of toxicity
I had a thought, and would be curious to see others' thoughts/debate on it.
In other games, such as Overwatch, HOTS, and DOTA2, leaving is not punished quite as drastically as in League. After 1 leaver, anyone can leave with lesser or no penalty. This is especially true in non-competitive modes, which, in some of those games, incur no penalty at all for leaving.
Is it possible that, due to players wanting to win and the higher chance (or perceived higher chance) of players simply leaving if there's toxicity in game, that players in those games are less toxic because they do not want their teammates to leave?
I am not saying such a system would work in League (in fact it would not, for multiple reasons), but it is a thought I had.