There was a time when official electronic communications weren’t encrypted, and the Secret Service that protects the president of the United States and other government officials chose code names for those they protected. The practice continues today, but it’s more for clarity and tradition. When you have a family of, say Trumps, you can’t just refer to a “Trump.” And for the sake of brevity, a code name like “Starfox” would be a lot faster when communicating than, say “Franklin Roosevelt.”
Also, as a nod to tradition, the code names for First Families stick to the same letter. Although most of those with code names are part of the president’s family, there are a handful who aren’t who were given new monikers.