Fat bikes are great where the tires actually provide advantage. But around here, a lot of casual cyclists are buying them because coolness. I see them on paved roads, and solid dirt and gravel surfaces where a lighter bike with reasonable tires would work perfectly well.

Again, they're great where they provide an advantage, but as general, all around bike, mho is not.

My guess is that people who can move a fat bike as fast as people on other bikes better suited to the terrain and surface are just stronger. Similar to why I get passed regularly by crappy, heavy mountain bikes ridden by backpack wearing college students in jeans when I'm riding my 16 pound road bike. It doesn't mean the mountain bike is just as good for riding on a road, it means they're stronger.

Again, jmho.