yes buddy i am aware of cursevoice and i use it :> the think is not everyone is using it.
They're not using it because they don't want to.
I know it must shocking to you, but some people don't want vocal communication with other people.
Do you know CurseVoice was 'illegal' for a while? If you had it installed, it automatically put everyone into a voice chatroom. It FORCED you to chat like this (to my knowledge it still does this with WoW. I've had to leave it when entering a battleground a few times).
Riot didn't like that players were being forced into an environment they couldn't police, so CV had to change the way their program worked or anyone found using it would be banned.
Why would Riot add their own version of this?