User blog comment:Gundam Legilis/Environmental Issues in RWBY/@comment-9090085-20150403210308/@comment-9090085-20150405174948

Well, we don't know how many Dust mines there are; there could be less then a dozen(or even half-dozen) worldwide. And/or the Schnee quarry is simply so massive that all other sources of Dust in the world combined don't even come to (say)half it's output.

Or something - at this point it's mostly just theorizing.