Were they really ever "The Fab Four?" The gossip media love to bestow nicknames upon people. They thought themselves clever to call these royals the "Fab Four," first actually the nickname for the Beatles, a highly successful, iconic musical group.
They really weren't the group that the press wanted you to believe. They had not been together long enough for all four to have worked together to do much. And, facing facts, William is future king and he and Catherine have their own agenda to look to; Harry will not be king and he and Meghan will have more freedom to pick and choose the work that they will do. With these diverging interests always being there, it was a certainty that the brothers would have to form their separate households to meet their needs.