I've never found the blank canvas argument all that compelling. It's a CRPG, your choices are always finite. The character is already written for you, you just get to choose which version it is.
It�s a thing. There more you define the character, the less space you leave for the player. Voicing a custom is especially troublesome as how do you voice a character without identity? All RPG and RPG-agecent titles with voice protagonist that worked provided heavily defined characters (Mass Effect, Witchers, Alpha Protocol). Personally I find games that try to voice protagonist and making it somewhat custom just end up with vague, off putting up charismatic git of a character, who provides little character, and prevents me from characterising him or her (Dragon Age Inquisition, Cyberpunk).
However, I didn�t find BG3 lending itself to roleplay anyway - so I don�t think voicing Tav would take away anything meaningful. His voice is present throughout anyway, so it�s not like one can use imagination too much.
That said. Voicing Protagonist would mean voicing all of the possible options, and all of the Origins. Also making a cutscene for every line spoken, for every variable of the character. That�s a staggering amount of work, so one has to wonder if it would be worth the effort. Larian has already pushing the envelope by having cinematics in a game with highly customisable protagonist.
