since this is rating traffic as % of total... I imagine this is less a result of "bittorrent is dying/nobody uses it" and more a result of "the rest of the internet traffic has grown exponentially with the availability of ubiquitous fast connections, while the number of bittorrent consumers has been roughly steady"
no shit BitTorrent was the majority of traffic in 2004. Most connected users were still using some form of DSL or low-bandwidth cable, and some of us were even still using ISDN/Dialup. Even youtube was still a pipe-dream, so most "normal" browsing folk were loading forum web pages with sizes <50k per page. Bittorrent allowing resilient, long-term downloads over slow pipes was the only thing that even EXISTED for bulk data transfer, and could saturate a pipe for days.