"true craft of spending years meticulously writing a novel" - tell this to Stephen King, who wrote some of his work in a year!!!
If you don't read that genre, like I often don't, I wouldn't have noticed this "theme" going on. "Hottest" theme is something almost everyone notices, despite preferred genre, such as the Twilight craze and the surge of hottest themes until that died down. Think about how much money those after books made, along with dystopian fiction which blasted onto our screens. And let's not forget what you describe as a number 1 could easily be someone's worst book ever.
I'm not sure what occupation has to do with it either. Unless famous, authors don't make a lot of money. A large portion goes to the publisher and their agent (if they have one) leaving them with about 10%. It's a business, and what sells will be published. Bandwagon or no.