I agree, it would be wonderful if Tav had a voice in dialogue. I was surprised when they hadn't.
However, I understand that it would have been a HUGE task! There's, what, six different voice options for Tav? Tav has at least as many lines as other characters combined - given that they are the other half of the conversation -, so recording all of that would've ment enourmously more work. Plus they probably should have also acted those lines out so that Tav would have movement when they say things, because it would probably be weird if Tav always talked off-camera.
I believe that Tav is also ment to be a blank canvas for the players headcanon. When they don't actually have a voice (nor bodylanguage when they are talking), there can't be clashes where the player disagrees with how the lines are acted out. I personally would have preferred for Tav to have a voice, since I always prefer a main character with actual personality over being a vessel, but I can see a point in this direction, too.
