I think it's just that FastTrack works better right now. People notice they get better results - they really don't have to understand why.

Gnutella was first, and FastTrack was designed to account for many of its weaknesses. The only problem is it's not an open protocol, and now that they use a central server for authorization, it can be shut down like any other private P2P network. I just hope Gnutella catches up to it in functionality before that happens.

Of couse people could start implementing gIFT based peers using the open version of FastTrack. True, it can no longer work with actual FT servers, but you could form a new, more functional, P2P network around the protocol.