Why is this the answer?

The answer is flag because this riddle is describing something that is often very high up and moves back and forth, like waving hello, but it cannot talk or make any sound at all. Let us look closely at the clues in the riddle. The first part says, "Up on high I wave away." Think about where you see a flag. A flag is almost always placed high up on a very tall pole, or sometimes on a ship's mast, so everyone can see it. It is usually way up in the air, closer to the clouds than you are! When the wind comes along, it catches the cloth of the flag, and the flag begins to flutter and move. This movement is the "waving" the riddle talks about. It looks like the flag is moving its whole body back and forth, just like you wave your hand when you say goodbye to a friend. The material is designed to flow freely and wave in the breeze. Now for the second clue: "but not a word can I say." A flag is a piece of fabric, like a big, beautiful piece of strong cloth. Even though it is super important and has special colors and designs to show what it stands for, it does not have a mouth or a voice box. It cannot talk, whisper, or shout. It is completely silent. The only sound you might hear is the "snap, snap, snap" of the fabric as the wind makes it move very quickly. The noise is from the cloth hitting the air, not from the flag actually speaking words. This makes the riddle a very clever word puzzle! It uses the word "wave" to trick your brain into thinking of a person or an animal, and then it reminds you that this waving thing is silent. The flag is doing a silent dance in the sky, always on high, always waving with the wind, but never, ever speaking. It is a fantastic example of a riddle that uses everyday actions to describe an ordinary object in a fun and surprising way. It has a special language all its own, communicated through its colors and symbols, but not with words. That is why the answer is a flag.