To be honest, its because he's a high profile drummer, is instantly recognisable, has extensive sponsorship with big/trendy companies and is always adding something tasteful and appropriate to whatever he's playing.
From a drummers perspective, he's phenomenal with what he can add to a song, but there are much better technical players out there. He's sometimes a little sloppy with rolls and such, but that's part of the beauty of his style.
Irrespective of whether you love or hate him, when he starts playing, you instantly know its him, and that's a big part of the reason I think.
Personally, he's one of my favourites, simply because of his style and stage presence, but he's not in any way the best drummer in the world.