You want to role play? You get some friends together and play P&P D&D, Traveller, Skyrealms of Jorune etc around a table. That's role playing. cRPGs are poor relations, because everything is done within the frame of the limited possibility space of the systems. You're in a prison cell, so claiming that lack of voice makes it somehow better is a fallacy. What computers are really good at doing is immersion and world building, those are the strengths of the medium. With something like Skyrim where it's ostensibly a first person viewpoint lack of a voice is ok because you are an anonymous cipher with no real personal commitments to whats going on. However that doesn't sit that well with games like The Witcher where in you play a specific character. There's more leg room in the latter type of game because the narrative can be personalized. The former is restrictive in terms of the degree of engagement it can elicit.
As for the why? Because they can. If the technologies of now were available back when Black Isle made the original fallout, do you think the game would still have been silent protagonist? Or do you think the dialogue would of been spoken? We're in an evolving medium and games are mechanistically a reflection of the capabilities of the technology available at the time of their creation.
That's about as proper as telling someone to watch a movie if they want their character more significantly pre-defined with everything voice-acted because that's immersion and the high-point of controlled and focused character interaction/world-building. No, what computers are good at is not immersion nor is it world-building, it's crunching numbers and accounting for user-inputted variables. Advances in those are what computers are inherently good at and the latter is what makes video games a great medium for interactivity and immersion by allowing the user to determine how they act or what they say in a game and allowing the game to properly respond. Protagonist voice-acting can limit the "immersion" factor by preventing the player from being able to insert their own attitude and tone towards what is being said and allowing themselves to feel as though they actually are the character. Forced character voice-acting does not promote immersion, it arguably detracts from it and world-building is an irrelevant and very vague concept that has no bearing on voice-acting. Just because the tangible interactivity allowed by the medium coupled with good storytelling inherently come at a price of role-playing flexibility relative to letting the imagination run wild doesn't mean developers need to throw caution to the wind and do whatever else they choose to further and needlessly take away certain elements of role-playing in video games (whatever those elements are deigned to be) "because they can". Just "Because they can" is a poor excuse to do anything and is counter-intuitive to good design in nearly any creative field. It also removes the potential for variability across different games by forcing the decision to all cRPGs just because it's possible.
There is a massive potential within computer games to allow a mix between full-blown imaginative role-playing and effective role-playing within the context of an intricate plot and character relations. That includes varying degrees in between depending on the game. Not every game is the same. For example, The Witcher 2 is based on a pre-existing book series with an already clearly-defined character. They could not have rightfully made the game any other way than having Geralt voiced, in my opinion, because I am a fan of the books and knew all along that Geralt is a very specifically-designed character with existing opinions, behavior trends, and disposition towards the world and its habitants. Geralt is not meant to be all that molded by the player and rightly so. But Geralt is not the usual case in RPGs and The Witcher 2's way of doing things is unique in the sense of adding on to a predefined character's story arch. Not every (story-focused, in this case) game needs or should do the same thing because that is not how a lot of even story-focused RPGs were designed. They were designed with an overarching and specific plot and had limits on character progression, but often allow you to shape the character how you see fit within limits for good reason and whether intentional or not (I would argue it varies, but that some are definitely intentional), the effect it had resonated with people. Forcing voice-acting, a name, or whatever else appeals to other people, but there is no valid way to claim it is objectively superior (especially not with what is effectively "well, if it's not to the same level as tabletop RPGs might as well limit it even further"). It
is a design choice, otherwise we would never have even had the choice of names or looks, or personality, or whatever in any of these games to begin with. Technology has not been a reason to forget voice-acting for a long time, it's nothing particularly advanced and everyone even back in KotOR
except the protagonist were voice-acted, for example. It's been easily possible for a long time, but voice-acting in general places restrictions on the complexity and variety of dialogue/dialogue trees due to cost and voice-acting on protagonists does further limit their own dialogue choices and remove a level of personal investment into the character.
Video games are an evolving medium, however the general direction in which something evolves does not necessarily cover all the untapped possibilities, justify the abandoned ones, or prove some objective superiority to the newer ones. Voice-acting is hardly an example of pure technical progression given that it's been possible with decent quality for quite a number of years and, more importantly, places restrictions on the variability and perception of certain mechanics in a subjectively understood way. Character voice-acting does not increase interactivity or engagement with the medium in any way. Even if it can be argued to give the in-game character more emotional definition, it actually restricts player involvement in doing so. You may prefer the former, other people prefer to view it as the latter. Either way, this is not a technical debate and there is no factual superiority to be argued in either argument. Different games can vary in where they fall on the spectrum of this balancing act between plot progression and character customization, of which neither will be fully realized to the same degree as in a dedicated medium.