Back when I was helping run Sacramento's Eclecticon, I was flying back from the 1991 Chicago Worldcon when I noticed that people claiming baggage from the same flight were wearing Chicon t-shirts. I didn't know these fans, but introduced myself and told them about Eclecticon. They said, effectively, "Thanks, but the only con we attend is Worldcon," even if there was a general SF convention in their figurative backyard.