Because normal human language doesn't describe things exactly and exhaustively specifying the edge cases; as soon as you need do that (and you do, in law, progr

Because normal human language doesn't describe things exactly and exhaustively specifying the edge cases; as soon as you need do that (and you do, in law, programming, math proofs, etc), even if you don't use a single specific term you get language that looks like legalese. In essence, none of the commonly used English words means exactly what you need to, so you need to add many explicit qualifiers to specify which parts of that wide and vague meaning shall apply and which shall not.