I'm fine with either, voiced or unvoiced. I think it all depends on how much a game wants to appeal to self-insert players.
Otome games tell a story from the perspective of a heroine, and since a big part of the target audience is women, they can relate to the protagonist. Giving players the option to change her name supports the part of the audience that prefers to self-insert (although you can still do that without changing the name).
So, I think that adding a voice to the MC limits the opportunity for self-insertion. For example, in Jack Jeanne, the protagonist is voiced for a good reason because she also sings in the story, and it's very focused on the protagonist's experience. Even so, you can keep her default name and mute her voice.
Sorry for my rambling, but I think that's a big reason why some MCs are voiced. It depends on the story and which audience the devs want to appeal to (still, you're free to self-insert or even create an OC, though that seems quite uncommon in the community)
It all comes down to each player's immersion. Recently, I noticed that some MCs have a birthday while others don't lol
Still, I read for R18, do the protagonists have a voice? I wouldn't particularly like to hear them in that sense :P