I think the Japanese Voice Acting is great, but I'm going to give the English voice acting a chance since I don't think the voice acting is as bad as people make it out to be. Of course, we all have our owns standards and expectations, but it can't be helped, unfortunately. At the very least, dual audio isn't something that was in the original game so it's not like we're losing content from the Japanese version.
Sure it was in Awakening, but I'm going to pin it on the fact that since it was supposed to be the last Fire Emblem in the series, they wanted to add as much extra content as they can and I do strongly agree that they probably went with this decision because of licensing issues with some of the bigger Japanese voice actors. I find that reasonable enough for its exclusion.