Pretty sure you nailed it. The only thing that's really going to top charts consistently is the music that appeals to a wide audience (pop). The problem may be that there are actually too many bands, and each band finds its niche via spotify, pandora, youtube, etc. The only bands that make it big are the guys (or gals) that appeal to a wide audience: Coldplay, Maroon 5, Imagine Dragons, and in the past few years Paramore, Kings of Leon. The only anomaly of late has been Mumford and Sons. They're the only band I can think of with such a different sound to find so much success.