I'll post what I did at another place regarding the whole thing. To put some context in it, someone said that Skullgirls had a lesser price tag on their voice work stretch goal.
The post:
They have to RE-create the scenes to work well with voice if they get their goal. Thats backtracking and more work than just adding a sound file playing every now and then. This could be new animation work, and new scripting work for two languages. That is if they want to do it right. On top of all this they have to re-schedule the whole thing mid development. Yeah, I can see it. It's probably rounded up a little, to allow for creative experimentation and unforeseen issues, but still. You want a high quality product right? You want it done right? That doesn't come cheap.
Compare that to Skullgirls where they inserted new sound effect files that happen to be recordings of people's voices, in a game where the fights already have sound effects playing. Not to mention full lines are considerably more expensive than a handful battle quips. You'll even need those as well for MN9, for the in game voices.
Game development isn't magic, or cheap. They are targetting April 2015 for release. The less your budget the less people you can hire, and the more work each person has to do, which takes a substantially larger amount of time. This is more and more true as games get more expensive to make, as player expectations are ever growing.