I think the main limitation would be cost.
Since the protagonist has multiple voice options to choose from, they would need to have ALL lines voiced multiple times, which adds up in cost pretty quickly.
Besides that, there's something about the "Blank Slate" protagonist they opted for. Giving more voiced dialogues could impact people's ability to project onto their character (It could be mitigated with Solasta style personality choosing, but that would require even more costs due to vastly increased dialogue amounts, multiplied by the number of protagonist voices)
Personally, I'd have preferred fully voiced protagonists, especially as I'm picking a voice for my character anyway for the random dialogues that occur when moving around. But I can see why it might not be feasible or desired by some.
