I believe it has something to do with Japanese players custom where they like to remain unannoymous, there was one drama back then in my JP LS, we usually use teamspeak to communicate and there was at least 4 females that speaks regularly.

One day, a new NA guy that joined the LS decided to stream his FFXIV without asking, so everything was leaked out, the players name, ingame chat, LS chat, their voices, and they gets so outraged.

On my point of view, it seems to be overreaction but i respect their choices. So this might be one of the consideration why you don't see JP multiplayer game supporting voice chat ingame.