Why does riot bans toxic players but not trollers that make good players become toxic ones.

Riot should ban troll players not just toxic people, because toxic people were good players once but trollers made them toxic, trollers ruining this game that used to be fun and awesome to play, now become lame every season cause of trollers ruining matches and trollers wont get ban wow that lame, Riot should step up their game and should ban trollers, trollers making good players become toxic and making good players quit this game, trolls every 2 out of 3 matches in rank, riot ban trollers, this is what i think, i used to love playing this game but now a troll comes in and ruins good players matches and trollers making players quit this game.