Video game studios often go cheap on things besides contractors, my experience from the inside is that the majority of voice talent is used outside the usual Hollywood system because they don't want to pay close to a union actor's competitive wages, and forget royalties for people who are not Hollywood famous. For instance, this is part of the reason Bill Roper is the voice of a lot of Warcraft 1 characters - they didn't want to pay professionals, and he was already there.

I haven't been on the inside in a while but we might have one musician on a AAA title and he/she would compose all the music and they might also do all the foley work because musicians you might have heard of would probably laugh at the wages and would demand royalties. Obviously part of the issue is making video games can be a crap shoot where a game with original IP is just as often a failure as a success so it can be hard to justify spending money on an unknown entity, and royalties don't exist except for bigger successes for the most part.