This scam has been around since long before AI voice was a thing. You say something scary enough, and people will subconsciously attribute anything off about the voice to a bad connection and the severe stress the person is presumably under and genuinely think the voice sounds exactly like their loved one. AI voice makes it easier to fool more people, but I bet most of these types of scammers are not putting in the time to research every target to build a voice profile and instead focus on calling as many people as possible. Of course, these days anyone taken by this scam will assume it must have been AI voice, because otherwise how did they sound so convincing.