i totally agree with you... now this is the reason they wont do it.. because riot balances the game at plat+ and at high level elo's there is a smaller player base.... just like a mountain....
so if you start banning the players at higher level elo then that means you make a small player bases even smaller, and if you are one of these players, who does not want to face another player you know to be good, say maybe because you stream and you make more money if you win a game, or destroy "noobs" you could just report them after a game.... then you would not have to play against them....
so a lil simply in numbers...
say i play in a top grp of 100 people
i lose to 50 of these people consistently
so i report these 50 people after every game i play against them, if im in a grp we can all report them
i no longer play against them in your system
i now win against this new smaller group of 50 a lot.... until these players start reporting me and not having to play against me....
so the system repeats.... the group gets smaller.... and we are left with no one playing the game.... or an error happening