The first implication of a reason, a comprehensible reason behind these transformations is fantastic. This is very rewarding, so many chapters into the story, to realize this wasn't a bizarre accident without explanation, but something more insidious is afoot. And it seems counter-intuitive that something as large as a giddy, hungry giantess could surprise anyone, but now it makes sense. And because it makes sense, it's that much scarier, that you could be doing your best to hide out and sneak around, and a giantess could zero in on you from out of nowhere.