Compared to the total number of users on the Internet relatively few have stable always-on machines ready to host P2P content. ISPs do not make it easy or at times possible to poke holes in firewalls to allow for easy hosting on residential connections. This necessitates hole punching which adds non-trivial delays on connections and overall poorer network performance.
It's less about imagination being dead but instead limitations of the modern Internet retards momentum of P2P anything.