Lanefan
Victoria Rules
Then perhaps those DMs aren't as good at it as maybe they think they are. DMing involves a great many skills, one of which (and arguably the most important of which) is adaptibility as evidenced by a willingness to abandon pre-laid plans.As I said, a much wider view of "I'll run any campaign that evolves" than I have any reason to believe any significant number of GMs are interested in.
It depends on the level of commitment the DM is willing to put in. There's many ways of running a split campaign - and I've probably done all of them over the years - and some of them don't involve much if any extra DM time.And most people aren't willing to run two campaigns if a split happens, either.
Me, I just assume the party is going to split at some point and stand ready for that eventuality.