"It was never really a question," Baldur's Gate III design producer David Walgrave said, according to USG. "We've been doing turn-based for a while now. We're pretty good at it. Dungeons & Dragons is turn-based in itself, so it makes a lot of sense."
In other words, we're doing turn based because we already know turn based, and in our unknowledgeable viewpoint, we think this is how D&D is supposed to be, so we're just going to shoehorn it in.
In a tabletop game, you use your imagination. We roll individually and speak one at a time because of the limits of the dungeon master and human speech. We don't actually imagine the action happening like in a turn based video game. All the action is happening simultaneously. In a video game, you have visual representation, so it should appear realistic. The rounds and turns in D&D are measurements of time and the actions performed, NOT a mandate to perform pugilistic kabuki theater.