Tor relies on exit nodes that are run by volunteers. These exit nodes are limited in both quantity and bandwidth and valuable for activists and others requiring high levels of privacy for the clearnet. I2P does not access the clearnet by default. Instead I2P is peer to peer focused and is setup ideally for torrenting privately. Basicaly Tor would be overloaded if it was used heavily for torrenting. I2P instead gets more robust with eachadditional user.