I haven't gotten too far in the storyline, but I'm sure they are saving their resources for more important parts of the story. Kinda like how older FF game would only go to CG scenes at bigger moments in the game.
This was an acceptable answer during the Sega CD days. Today's gamers expect more, especially with what BioWare is doing (in offline games as well as their new MMO).
I kind of felt like I did with Dragon Quest VIII. If you are just going to use a tiny bit of voice acting, I would rather you just leave it out altogether.