A lot many individuals run TOR exit nodes, but I never hear about people running their own I2P outproxies. Is it really hard to host, or is there some other reason? I thought that if you could run a TOR exit node I'd think you'd be just fine running an I2P outproxy.

Running more outproxies will help in bridging torrents from the clearnet to I2P, which would be a very good move considering the crackdowns on torrents right now. Companies even want to involve civilians into their lawsuits in Sweden now, making the need for privacy/anonymity even more important when torrenting, which I2P provides.