It just happens to be what the wider public also loves. Because the reading public is smart. They can spot an impostor a mile away. Write what you love. The reading public will be able to smell your enthusiasm and they will leap aboard for the ride.
Publicity sells books.
But that Millionaire thing is getting almost as played out as the whole Chicken Soup book series. But seriously, my advice to any new author is to come up with an interesting slant about your book that makes a good angle to sell it. Being a good marketer can be more important than being a good writer - sad but true. I became a de facto relationship expert after my book hit the stores. That got me on TV, radio, and in bookstores nationwide.