I disagree that suits won't put bad dialogue into a game. It's on "the check-list" now, and suits don't actually play the games, so as long as it's there they don't care!
Except if it makes the dialogue impracticably complex. How many people are going to bet for fully-voiced dialogue trees versus next generational graphics? That's the sort of complexity that would be necessary to add an actor's voice to thousands upon thousands of lines with slightly different variables. Permutations add up: four classes, three alignment choices and two actions for one character makes twenty four (four times three times two times one, or 4!) voice tracks for one dialogue. Multiply that by hundreds of dialogues and more options (say five classes and four alignment choices: lawful good, chaotic good, brute bully and sneaky evil), two actions, and you have 5!