Cost and scale. HTTP video is significantly cheaper to deliver because of the robust and competitive CDN market.
You can deliver all your video via WebRTC with lower latency, but your bandwidth bill will be an order of magnitude higher.
You can deliver all your video via WebRTC with lower latency, but your bandwidth bill will be an order of magnitude higher.
But even then, many CDNs CAN "stream" using chunked transfer encoding.
As the article says, HLS or DASH are specifically about not having to suffer through buffering by auto-dialing quality down, otherwise you can also start viewing during download with the browser <video> tag, over FTP with VLC, or even with peer to peer software like eMule or torrents !
I'm not sure what "real" streaming would even be ? (It probably wouldn't be over HTTP...)