Why? Here's why, because these keyboard warriors are cowards, ineffectual losers with nothing going on. They live in Mommy's basement, have Cheeto dust and Dorito crumbs in their chest hair and haven't been laid since Regan was president, or ever.
Your wife, being, you know, human, exposed a vulerability by expressing her worry, the trolls smell that, deterine it's weakness and pounce so they can feel big and powerful for a moment. They have so little power in their own lives thats what they do. I guarantee you not one of these idiots would walk up to her face and say any of the things they said.