It's not money/development time/resources that concern me. Digital recording is pretty easy in this day and age. And while I'm sure it adds costs beyond money, i'm not sure its as much as is being made out in this thread- but whatevs, this isn't the reason to not add PC voice.
I say "Hell Nah!" mostly because I don't want canned voices in place of my minds ear regarding a character that is mine to customize and play out.
Sure, games like Saints Row use a pitch shifter to give variance in voice tone, but it's pretty a noticeable effect. I prefer, by far, reading out what my PC is saying in whatever pitch, timbre, accent, inflection etc. I decide that MY PC would use.
Aside from that, I don't want to spend the time that it would take my PC to say all of these lines throughout the entire game. I am already reading all of them in order to decide which dialogue I want to reply with. What exactly is the incentive of hearing the choice I have already made and voiced in my minds ear? No new information/content is being given with it, and now I have to sit and wait until the PC speaks their lines, before I hear the reply from the NPC? I am all for deep dialogue, but it's an unnecessarily redundant micro transaction time sink, that actually takes from immersion.