Why is this the answer?

The answer is mountain because this clever riddle uses fun word pictures to describe one of the biggest and most amazing things on Earth. It wants you to think about a mountain in a new and surprising way, comparing it to things that are alive even though it is just made of rock and dirt. This puzzle is trying to trick you by using words like "roots" and "grows" that usually only describe living things. Let us look at the first clue, "What has roots as nobody sees." When you hear the word "roots," you probably picture a big tree. A tree's roots are hidden deep in the ground, and you cannot see them from above. A mountain is the same way! It has a giant base that goes far down into the ground beneath the crust of the earth. Scientists call this its "root system." It is a massive, solid part of the earth that anchors the whole mountain, but it is completely hidden, so nobody sees it. It is like the secret foundation of the huge rock structure. Next, the riddle says, "is taller than trees." This clue is a little easier to guess! Mountains are much taller than any tree you have ever seen. They stand proudly above the tallest forests. A tall tree might be a hundred feet high, but a large mountain can be thousands of feet high, reaching way up into the sky where the air is cold and sometimes covered in snow. This incredible height makes the mountain easy to spot from a long distance. Finally, the riddle asks, "Up, up it goes, and yet never grows?" A mountain definitely goes "Up, up it goes," towering toward the clouds, but it is a giant rock, not a living thing, so it never gets taller each year like a person or a flower does. Even though mountains are created over millions of years by powerful earth movements, once they are formed, their height stays the same. That is the perfect way to describe a huge, strong mountain! It is a massive, unchanging giant.