New voices, new backgrounds..
That would not be very easy considering the existence of personal drivel. Not only does voices for various grunts and shouts and so on need to be added, but each line in each path of the fully voice-overed personal drivel needs to be voiced as well.
Furthermore since you are asking for more backrounds, that would mean more personal drivel paths would have to be added. If each race/gender combo would have 3 voices each, that would mean each new character backround would have to be voice overed 6 times.
Point is: It is too much work for too little payoff.
I would imagine that they’d put their voice resources to work on new races rather than just more voices for existing races. Either way its going to be a lot of work, but it pays off a bit better with a completely new race.