As proven in this thread, the many accounts of people assuredly disregarding players who cannot use voice chat as an option and choosing to 100% neglect them could be a factor why SE thought it would be a good idea to leave it out of the game.

It's alright to degree to have your preference but simple chat can get the job done in a crunch. It is by no means 100% a must to have voice chat in this game, hence it not being function in it. It's the players attitudes that decide to not allow others join them because they have deemed them unworthy of there time.

A very sad truth how peoples heads turn for the worse towards one another in a video game meant for fun.

Mute/deaf people are out of luck of the bat aswell to be treated so poorly.