The entire point of being a voice actor is that you can act using just your voice. A 30 year old can make themselves sound like an 80 year old, a 20 year old can make themselves sound like an 8 year old. The creators landed on these actors after they found the performances they were looking for. I seriously doubt there was any thought put into it beyond that. I think creators should always have the final say when it comes to creating their work. From a statistical standpoint it would be nice for them to go out of there way to help groups with less opportunity, but I'm not going to tell them how to make their thing.