Probably the biggest issue is what's involved in modding SF. Altering the existing campainges is fairly straight forward. but as we've found working on the SW to SF mod, from scratch, there is a lot involved.
Mind you, we are going pretty Monty Haul on SW to SF. I'm not sure about the others in our group, but I've really learned a lot in the past couple months about modding SF. Thanks to CK and SJ's invaluable knowlege.