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.
