You don't even have a reason.
Ok fair enough.
I dont want to have every thing in the game walking up and talking to me in a voice that sounds like schema in a state of catatonic depression, recorded at 2am on a web cam mic.
Making voice audio isnt some simple fast thing if it is to be done correctly, and if one does not have an audiogenic voice (yes i made that word up) then they simply don't.
Blowing the budget to hire some voice actors, and stopping everything to write scripts, do recording sessions, code the voice scripts into the game etc puts everything else on the back burner.
And for what at this point?
It hasn't furthered the game mechanics, hasnt gotten in any new playability feature, hasnt optimised MP servers, or an endless list of other things.
It didnt contribute to taking the current game forward.
Any of the things where i can see voice being a great addition to the game, dont even exist in the game yet to add voice to.
Id rather have those built 1st.