FEASIBILITY is the name of the issue here
It's not really FEASIBILITY that's the issue.
It's very feasible. That's why so many games have fully voiced protagonists.
The crux of the issue is making that decision of "This is a video game, so this is your character" or "Lets make you the least defined entity in existence so you can headcanon in something"
Feasibility only comes in as a factor when deciding on "Lets make you the least defined entity in existence" but also trying to allow you to personally define your character.
Meanwhile, every game ends up with "This is a video game, so this is your character" because that's the nature of having a predetermined narrative. Some people try to deny this by pretending that the written dialogues are something else, but the game will simply continue on with your character being a predefined character (To a degree determined by how extensive the actual dialogue options are)
Some people will prefer the wishy-washy notion of being undefined as a character and detracted from the actual world in order to pretend a video game is a TT game where you can actually be whatever you want in the story.
While others will accept the nature of video games being pre-defined and simply want their character (Whomever it was written to be) to be integrated into the world as fully as possible.
It's simply up to developers to decide which crowd they want to appeal to (Where I can imagine the former would take precedent due to it being far easier and cheaper to simply not animate and voice the PC during dialogues)
There's no limitations at play here. Even when it comes to dialogue options, there's nothing limiting the options available for voiced/unvoiced other than things simply not being written and the budget to hire VA's to record all the lines (And to a lesser extent, the decision to move towards "Dialogue Wheels" that have limited space for options and are simply awful design compared the the classic list of options which can be infinitely long...)
Maybe somewhere down the line, when AI has all but replaced every aspect of our lives, we'll get that idealized scenario of being able to make your own custom character with the narrative being altered based on specifically your decisions with your character whereby AI writes the narrative as you engage with the game and also voices your character based on what you imagine...
