BitTorrent isn't particularly efficient; a well-designed CDN beats it every time, and is pretty cheap these days. (Generally, you get random peers, not peers that are particularly close to you. You could try to fix that, but you'd quickly end up with second-order problems around e.g. which peers have which chunks.) Which is precisely why you're not seeing much adoption outside the warez scene—they're the only ones for which that kind of decentralization is more important than reliable, fast downloads.