With Oblivion in particular I think they threw a ton of money to get Patrick Stewart to voice a few lines. That could have done towards hiring many voice actors

With Oblivion in particular I think they threw a ton of money to get Patrick Stewart to voice a few lines. That could have done towards hiring many voice actors, but it may have been a reasonable marketing move overall - it's hard to tell given the shape of the market and that genre at the time.