Have you never wondered why Comander Sheppard have rarely more than 3 options, of wich they are all the same and differs only in flavour?
I mean ... even Renegade and Paragon were basicaly just "rough good soldier" and "friendly good soldier" when you think about it.
Voice is the reason ...
There is some connection to be made between fully voiced protagonist (and full VO in general) and less complex RPG, but I question whenever it is causality, or simple games that go for that kind of production value just don’t aim for branching dialogues.
Bioware is an especially troublesome studio to bring up, as their games were never particularly robust dialogue tree wise. The trend you mention can be easily traced as far as KOTOR, if not even Baldur’s Gate1&2. Their titles usually had two binary characters you could play as, but the conversation wheel made it a bit more obvious.
And as I mentioned before even of protagonist stays silent, in BG3 he still needs to be complemented by fully voiced and animated response by other NPCs making it far more tricky than creating few new nodes in the dialogue editor. Still, with voiced customs and origins, we would be looking at 10+ voice actors to record the same line. That would be an insanely silly thing to do.
