Because unlike other "social behaviour experts" on internet I don't know the viable solution? I just point out what doesn't work.
Well, when it comes to really competitive games it seems that when you do it with random people there will always be problems. As I've said before, when there is conflict of skill level and gaming goals there will be negative emotions. People dislike to feel that their time is being wasted and that is when they act out. And more often than not the actions are not intended but simply acted out on an impuls (
https://en.wikipedia.org/wiki/Hanlon's_razor). Those who intend to be assholes are minority and will do that no matter what.
So if we take into account that people most often do stupid things out of frustration, what do you think punishment will cause them to feel? More frustration -> more stupid behavior.
Yesterday I've listened to interesting thoughts of one of Polish youtubers (an older guy) about toxicity in Overwatch. He pointed out that it is an issue but actually had some really interesting proposals because instead of focusing on how to punish people he tried to understand why people act in certain manner. The baseline was that the game stops being enjoyable (and causes frustration) when your personal effort means little for you personal progression and you are constantly punished by how bad other people in your team are. And while he personally doesn't act that frustration out in game he noticed he is acting it out on his family. And therefor he doesn't play OV much anymore. This is just one opinion but I find certain validity in it because it tries to tackle the whole picture and our own flaws as human beings instead of just pushing the blame "on those evil people over there". Imagine that people are not assholes without a reason. If you really want something to change in that manner it would be good to understand that reason instead of looking for the easy solution that doesn't require any work. Those generally don't exist.
This is the main issue of random matchmaking.
The only way players can influence it on their own is by playing with friends or other organized groups. It's the same reason why no one pugs the hardest content in WoW until it can be heavily overgeared - it would be so frustrating that no one in their right mind would be willing to give any effort.