I’ve long wondered what would motivate a God to speak definitively to a select number of people at only one defined period in history…and never have returned to do it again. Further, if someone were to assert that God had spoken directly to them in this day and age, they would likely be determined mentally incompetent

I would say go with the obvious answer. The bible is nothing more than people trying to explain the natural world around them. The same as Greek mythology and Native American folk-lore.