Due to the increasingly poor behavior in the League of Legends public chat rooms, Riot Games has made the decision to shut chat rooms them down. They will remain disabled for the foreseeable future until the studio can create a public chat room that is able to handle "unwelcome drop-ins and toxic behavior."
Riot Games made a statement on the League of Legends forums that listed some longstanding issues that have run rampant within the public chat rooms that they hope to address. These issues include Riot Point sellers, Elo spams to boost a player's rating, and general unsportsmanlike behavior. The studio also wants to create better tools for moderation both public and private chat rooms as well as community hubs beyond the usual ignore button.
While the popularity of League of Legends has grown, so has its unsportsmanlike behavior. With Riot Games' push towards a more friendly public chat room, perhaps the studio can come closer to a more welcoming and enjoyable online experience.