Riot Games appears to have changed its mind about how they see voice chat. Originally set strongly against it, Riot has opened up and expressed that it's interested in possibly implementing a voice chat for League of Legends in the future.
In the past, our stance on voice comms emphasized the increased potential for negative behavior. We've since reconsidered our philosophy around voice chat and while there are some challenges we want to overcome (keeping it an opt-in experience, for example), we want to do it.
We believe League as a team sport should reward coordination, and that voice chat is a valuable tool for getting teams (and strangers) aligned. We'll probably begin deeper investigations once the League Client update is in a stable release so we don't have to build the feature twice, but hopefully this is a clear update on our philosophy and where we stand. We'll also give you further updates when the time comes.
- an "Ask Riot" blog post
In-game voice chat was always one of those things that the player-base has begged for. Right next to sandbox mode, it was the thing that players wanted but knew they probably weren't ever going to get it.
In the past, Riot has always been against voice chat, because it fundamentally breaks one of its major beliefs: Players should not have to mute or block other people for being toxic. By encouraging players to mute others, it enforces the idea that it's okay to be toxic, because you can just be ignored.
They also didn't want to ignore their female fanbase. In a past Reddit thread about voice chat, former Riot employee Jeffrey "Lyte" Lin posted about how voice chats tend to lead to 300 percent more toxicity towards females. (Since then, his Reddit account has been deleted.)
Generally voice-chats don't lead to more toxicity as a whole. Being mean on the Internet is easy when you can just type out comments, but it's much harder to say harsh words to somebody than to type them out.
Tons of online games have opt-in voice chat. Dota 2, Counter-strike: Global Offensive and Overwatch all have voice chat and it makes sense given that you need to work as a team in order to win in these games. It's no different in League. You need to work together and coordinate rotations, fights and objective-control in order to actually win.
In fact, Overwatch has been creeping in on League lately, especially in Korean PC-Bangs. An imgur post from Reddit shows that Overwatch coming close to topping League's amount of PC-Bang play-time. In one PC-Bang chain, Overwatch has surpassed League!
Overwatch's voice chat is successful because of how optional it is. You can turn it off, preventing you from ever joining the voice-chat at all, or you can opt-in for it and discuss strategy with your teammates. Nobody feels obligated to listen to anyone, ever.
Though the growing popularity of Overwatch and Riot not wanting League of Legends to fall behind could be a factor in why it's finally implementing voice chat, it's too early to say.